Accounting Policies [Abstract] Significant Accounting Policies [Table] Significant Accounting Policies [Table] Significant Accounting Policies [Table] Phase-in time period [Axis] Phase-in time period [Axis] The time periods to phase-in of the competitive bidding structure Year [Domain] Year [Domain] Year Year 2016 [Member] Year2016 [Member] Year 2016 Adjustments for New Accounting Pronouncements [Axis] Adjustments for New Accounting Pronouncements [Axis] Type of Adoption [Domain] Type of Adoption [Domain] Adjustments for New Accounting Pronouncement [Member] Adjustments for New Accounting Pronouncement [Member] Credit Facility [Axis] Credit Facility [Axis] Credit Facility [Domain] Credit Facility [Domain] Line of Credit [Member] Line of Credit [Member] Legal Entity [Axis] Legal Entity [Axis] Entity [Domain] Entity [Domain] THE DAYTON POWER AND LIGHT COMPANY [Member] Subsidiaries [Member] Significant Accounting Policies [Line Items] Significant Accounting Policies [Line Items] [Line Items] for Significant Accounting Policies [Table] Number of reportable segments Number of Reportable Segments Approximate number of retail customers Number Of Retail Customers This element represents the approximate number of retail customers that electricity is generated and distributed within the company's service territory. Service area, square miles Service Area Square Miles Service area square miles Electric generation through competitive bid Electric generation through competitive bid The percentage of electric generation for SSO customers through a competitive bidding process Entity number of employees Entity Number of Employees Employees under a collective bargaining agreement which expires in October-2011 Percentage Of Employees Under Collective Bargaining Agreement Percentage Of Employees Under Collective Bargaining Agreement Number of generating facilities Number Of Generating Facilities Number Of Generating Facilities Excise taxes collected Excise Taxes Collected Current portion of deferred finance costs Deferred Finance Costs, Current, Net Noncurrent portion of deferred finance costs Deferred Finance Costs, Noncurrent, Net Description of Business Nature of Operations [Text Block] Financial Statement Presentation Basis of Accounting, Policy [Policy Text Block] Accounting for Taxes Collected from Customers and Remitted to Governmental Authorities Regulatory Income Taxes, Policy [Policy Text Block] Recently Issued Accounting Standards New Accounting Pronouncements, Policy [Policy Text Block] Statement of Financial Position [Abstract] Statement [Table] Statement [Table] Statement [Line Items] Statement [Line Items] Common stock, shares authorized Common Stock, Shares Authorized Common stock, shares issued Common Stock, Shares, Issued Common stock, shares outstanding Common Stock, Shares, Outstanding Common stock, par value (in USD per share) Common Stock, Par or Stated Value Per Share Segment Reporting [Abstract] Schedule of Segment Reporting Information, by Segment [Table] Schedule of Segment Reporting Information, by Segment [Table] Segment Reporting Information [Line Items] Segment Reporting Information [Line Items] Number of operating segments Number of Operating Segments Number of coal fired power plants Number Of Coal Fired Power Plants Number Of Coal Fired Power Plants Related Party Transactions [Abstract] Schedule of Related Party Transactions, by Related Party [Table] Schedule of Related Party Transactions, by Related Party [Table] Related Party Transaction [Line Items] Related Party Transaction [Line Items] Related Party Transactions Related Party Transactions Disclosure [Text Block] Discontinued Operations and Disposal Groups [Abstract] Discontinued Operations Disposal Groups, Including Discontinued Operations, Disclosure [Text Block] Fair Value Disclosures [Abstract] Fair Value Measurements, Recurring and Nonrecurring [Table] Fair Value Measurements, Recurring and Nonrecurring [Table] Public Utility [Axis] Public Utility [Axis] Utility Plant [Domain] Utility Plant [Domain] Stuart [Member] Stuart [Member] Stuart [Member] Zimmer [Member] Zimmer [Member] Zimmer [Member] Killen [Member] Killen [Member] Killen [Member] Peaking Generating Facilities [Member] Peaking Generating Facilities [Member] Peaking Generating Facilities [Member] Measurement Frequency [Axis] Measurement Frequency [Axis] Fair Value, Measurement Frequency [Domain] Fair Value, Measurement Frequency [Domain] Fair Value, Hierarchy [Axis] Fair Value, Hierarchy [Axis] Fair Value Hierarchy [Domain] Fair Value Hierarchy [Domain] Fair Value, Inputs, Level 1 [Member] Fair Value, Inputs, Level 1 [Member] Level 2 [Member] Fair Value, Inputs, Level 2 [Member] Level 3 [Member] Fair Value, Inputs, Level 3 [Member] Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] Property, Plant and Equipment, Net Property, Plant and Equipment, Net Property, Plant, and Equipment, Fair Value Disclosure Property, Plant, and Equipment, Fair Value Disclosure Impairment of Long-Lived Assets Held-for-use Impairment of Long-Lived Assets Held-for-use Current Income Tax Expense (Benefit), Continuing Operations [Abstract] Entities [Table] Entities [Table] Entity Information [Line Items] Entity Information [Line Items] Schedule of Effective Income Tax Rates Schedule of Effective Income Tax Rates [Table Text Block] Schedule of Effective Income Tax Rates [Table Text Block] Contractual Obligations, Commercial Commitments And Contingencies [Abstract] Contractual Obligations, Commercial Commitments and Contingencies [Abstract] Contractual Obligations, Commercial Commitments and Contingencies Commitments and Contingencies Disclosure [Text Block] Long-term Debt, Current and Noncurrent [Abstract] Schedule of Long-term Debt Instruments [Table] Schedule of Long-term Debt Instruments [Table] Debt Instrument [Line Items] Debt Instrument [Line Items] Debt Obligations Long-term Debt [Text Block] Effective income tax rates Effective Income Tax Rate Reconciliation, Percent Estimated annual effective income tax rate Estimated Annual Effective Income Tax Rate, Continuing Operations A ratio calculated by dividing the estimated amount of annual income tax expense attributable to continuing operations by GAAP-basis estimated annual pretax income from continuing operations. General Discussion of Derivative Instruments and Hedging Activities [Abstract] Fair Values Derivatives, Balance Sheet Location, by Derivative Contract Type [Table] Fair Values Derivatives, Balance Sheet Location, by Derivative Contract Type [Table] Additional Collateral, Aggregate Fair Value, OTC Commodity Derivatives Additional Collateral, Aggregate Fair Value, OTC Commodity Derivatives The aggregate fair value of additional assets that would be required to be posted as collateral for derivative instruments with credit-risk-related contingent features if the credit-risk-related contingent features were triggered at the end of the reporting period - specifically related to OTC commodity derivatives. Fair value of commodity derivative instruments Derivative Liability, Fair Value, Gross Liability Collateral Already Posted, Aggregate Fair Value Liability position offset by the asset position of counterparties with master netting agreements Derivative Liability, Fair Value, Amount Offset Against Collateral Collateral if debt were to fall below investment grade Additional Collateral, Aggregate Fair Value Statement of Comprehensive Income [Abstract] Net income Net Income (Loss), Including Portion Attributable to Noncontrolling Interest Available-for-sale securities activity: Other Comprehensive Income (Loss), Available-for-sale Securities Adjustment, Net of Tax [Abstract] Change in fair value of available-for-sale securities, net of income tax Other Comprehensive Income (Loss), Unrealized Holding Gain (Loss) on Securities Arising During Period, Net of Tax Reclassification to earnings, net of income tax Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI for Sale of Securities, Net of Tax Total change in fair value of available-for-sale securities Other Comprehensive Income (Loss), Available-for-sale Securities Adjustment, Net of Tax Derivative activity: Other Comprehensive Income (Loss), Derivatives Qualifying as Hedges, Net of Tax [Abstract] Change in derivative fair value, net of income tax Other Comprehensive Income (Loss), Unrealized Gain (Loss) on Derivatives Arising During Period, Net of Tax Reclassification of earnings, net of income tax Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI on Derivatives, Net of Tax Total change in fair value of derivatives Other Comprehensive Income (Loss), Derivatives Qualifying as Hedges, Net of Tax Pension and postretirement activity: Other Comprehensive (Income) Loss, Pension and Other Postretirement Benefit Plans, Adjustment, Net of Tax [Abstract] Reclassification to earnings, net of income tax Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI, Pension and Other Postretirement Benefit Plans, for Net Transition Asset (Obligation), Net of Tax Total change in unfunded pension obligation Other Comprehensive (Income) Loss, Pension and Other Postretirement Benefit Plans, Adjustment, Net of Tax Other comprehensive income / (loss) Other Comprehensive Income (Loss), Net of Tax Net comprehensive income / (loss) Comprehensive Income (Loss), Net of Tax, Including Portion Attributable to Noncontrolling Interest Organization, Consolidation and Presentation of Financial Statements [Abstract] Accumulated Other Comprehensive Income (Loss) [Table] Accumulated Other Comprehensive Income (Loss) [Table] Equity Components [Axis] Equity Components [Axis] Equity Component [Domain] Equity Component [Domain] Gains / (losses) on available-for-sale securities [Member] Accumulated Net Investment Gain (Loss) Attributable to Parent [Member] Gains / (losses) on cash flow hedges [Member] Accumulated Net Gain (Loss) from Cash Flow Hedges Attributable to Parent [Member] Change in unfunded pension obligation [Member] Accumulated Defined Benefit Plans Adjustment Attributable to Parent [Member] Accumulated Other Comprehensive Income (Loss) [Line Items] Accumulated Other Comprehensive Income (Loss) [Line Items] AOCI Attributable to Parent, Net of Tax [Roll Forward] AOCI Attributable to Parent, Net of Tax [Roll Forward] Balance, beginning of period Accumulated Other Comprehensive Income (Loss), Net of Tax Other comprehensive income before reclassifications Other Comprehensive Income (Loss), before Reclassifications, Net of Tax Amounts reclassified from accumulated other comprehensive income / (loss) Reclassification from AOCI, Current Period, Net of Tax, Attributable to Parent Balance, end of period General Discussion of Pension and Other Postretirement Benefits [Abstract] Schedule of Defined Benefit Plans Disclosures [Table] Schedule of Defined Benefit Plans Disclosures [Table] Defined Benefit Plans and Other Postretirement Benefit Plans [Axis] Defined Benefit Plans and Other Postretirement Benefit Plans [Axis] Defined Benefit Plans [Domain] Defined Benefit Plan and Other Postretirement Benefit Plan [Domain] Pension [Member] Pension Plan [Member] Postretirement [Member] Other Postretirement Benefit Plan [Member] Contributions by employer Defined Benefit Plan, Contributions by Employer Service cost Defined Benefit Plan, Service Cost Interest cost Defined Benefit Plan, Interest Cost Expected return on assets Defined Benefit Plan, Expected Return on Plan Assets Prior service cost Defined Benefit Plan, Amortization of Prior Service Cost (Credit) Actuarial loss / (gain) Defined Benefit Plan, Amortization of Gains (Losses) Net periodic benefit cost Defined Benefit Plan, Net Periodic Benefit Cost Document and Entity Information [Abstract] Entity Registrant Name Entity Registrant Name Entity Central Index Key Entity Central Index Key Document Type Document Type Document Period End Date Document Period End Date Amendment Flag Amendment Flag Current Fiscal Year End Date Current Fiscal Year End Date Entity Current Reporting Status Entity Current Reporting Status Entity Filer Category Entity Filer Category Entity Common Stock, Shares Outstanding Entity Common Stock, Shares Outstanding Document Fiscal Year Focus Document Fiscal Year Focus Document Fiscal Period Focus Document Fiscal Period Focus Entity Voluntary Filers Entity Voluntary Filers Entity Well-known Seasoned Issuer Entity Well-known Seasoned Issuer Public Utility, Property, Plant and Equipment [Table] Public Utility, Property, Plant and Equipment [Table] Investment, Name [Axis] Investment, Name [Axis] Investment, Name [Domain] Investment, Name [Domain] Electric Generation Company [Member] Electric Generation Company [Member] The Electric Generation Company DP&L holds a 4.9% interest. Debt Instrument [Axis] Debt Instrument [Axis] Debt Instrument, Name [Domain] Debt Instrument, Name [Domain] Debt Obligation on 4.9% Equity Ownership [Member] Debt Obligation On49 Equity Ownership [Member] Debt Obligation on 4.9% Equity Ownership in an electric generation company DPLE [Member] Dple [Member] DPLE member without DPLER Public Utility, Property, Plant and Equipment [Line Items] Public Utility, Property, Plant and Equipment [Line Items] Third party guarantees Disclosure Other Third Party Guarantees Amount This item represents the amount of total guarantees provided to third parties for future financial or performance assurance. The guarantees are provided to enhance the creditworthiness attributed DPL's subsidiaries, DPLE and DPLER, on a stand-alone basis. Any, against the loss of value in the underlying assets in the security which were considered and relied upon as one of the potential factors in reaching a conclusion that the available-for-sale investments are not other-than -temporarily impaired. Due to third parties, current Due to third parties current Due to third parties current. Equity ownership interest Public utilities equity interest, cost method, percentage The noncontrolling equity interest in an electric generation company, accounted for under the cost method of accounting. Equity ownership interest aggregate cost Equity Method Investment, Aggregate Cost Debt obligation Long-term Debt and Capital Lease Obligations Debt maturity, earliest Long Term Debt Date Range Equity Ownership, Start Long Term Debt Date Range Equity Ownership, Start Debt maturity, latest Long Term Debt Date Range Equity Ownership, End Long Term Debt Date Range Equity Ownership, End Schedule of New Accounting Pronouncements Schedule of New Accounting Pronouncements and Changes in Accounting Principles [Table Text Block] Financial Reporting for Reportable Business Segments Schedule of Segment Reporting Information, by Segment [Table Text Block] Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Table] Long-term debt, earliest maturities Long Term Debt Range Adjusted To Fair Value at Merger Start Long Term Debt Range Adjusted To Fair Value at Merger Start Long-term debt, latest maturities Long Term Debt Range Adjusted To Fair Value At Merger End Long Term Debt Range Adjusted To Fair Value At Merger End Unrealized gains in AOCI, before tax Unrealized Gains in AOCI, Before Tax Unrealized Gains in AOCI, Before Tax Unrealized gains in AOCI, net of tax Unrealized Gains in AOCI, Net of Tax Unrealized Gains in AOCI, Net of Tax Unrealized gains and immaterial unrealized losses in AOCI, before tax Unrealized Gains and Immaterial Unrealized Losses in AOCI, Before Tax Unrealized Gains and Immaterial Unrealized Losses in AOCI, Before Tax Unrealized gains and immaterial unrealized losses in AOCI, after tax Unrealized Gains and Immaterial Unrealized Losses in AOCI, Net of Tax Unrealized Gains and Immaterial Unrealized Losses in AOCI, Net of Tax Unrealized losses in AOCI, before tax Unrealized Losses in AOCI, Before Tax Unrealized Losses in AOCI, Before Tax Unrealized losses in AOCI, net of tax Unrealized Losses in AOCI, Net of Tax Unrealized Losses in AOCI, Net of Tax Realized gains on investments sold to facilitate the distribution of benefits Available-for-sale Securities, Gross Realized Gains (Losses), Sale Proceeds Realized gains on investments sold to facilitate the distribution of benefits, after tax AvailableForSaleSecuritiesGross Realized Gains Losses Sale Proceeds Net of Tax Realized gains and losses from sale of available for sale securities, net of tax. Percent of inputs to the fair value of derivative instruments from quoted market prices (percent) Percentage Of Inputs To The Fair Value Of Derivative Instruments From Quoted Market Prices Percentage Of Inputs To The Fair Value Of Derivative Instruments From Quoted Market Prices Gross additions to our existing landfill and asbestos AROs Costs Incurred, Asset Retirement Obligation Incurred Fixed-asset Impairment [Abstract] Fixed-asset Impairment [Abstract] Schedule of Finite-Lived Intangible Assets [Table] Schedule of Finite-Lived Intangible Assets [Table] Finite-Lived Intangible Assets [Line Items] Finite-Lived Intangible Assets [Line Items] Asset Impairment Charges [Text Block] Asset Impairment Charges [Text Block] Supplemental Financial Information [Table] Supplemental Financial Information [Table] Supplemental Financial Information [Table] Supplemental Financial Information [Line Items] Supplemental Financial Information [Line Items] [Line Items] for Supplemental Financial Information [Table] Schedule of Supplemental Financial Information Schedule Of Supplemental Financial Information [Table Text Block] This element may be used to describe the supplemental financial information of the reporting entity as a single block of text. Reclassification out of Accumulated Other Comprehensive Income Reclassification out of Accumulated Other Comprehensive Income [Table Text Block] Schedule of Accumulated Other Comprehensive Income (Loss) Schedule of Accumulated Other Comprehensive Income (Loss) [Table Text Block] Accounts receivable, net Disposal Group, Including Discontinued Operation, Accounts, Notes and Loans Receivable, Net Unbilled revenue Unbilled Revenue Amounts due from customers based upon an estimate of sales of power to customers since the last customer billing. Customer receivables Customer receivables Amounts due from customers for billed utility services. Amounts due from partners in jointly owned stations Amounts due from partners in jointly-owned plants Amount of receivables due from partners in jointly-owned plants, due within 1 year (or 1 business cycle). Other Other Receivables Provision for uncollectible accounts Allowance for Doubtful Accounts Receivable Total accounts receivable, net Receivables, Net, Current Fuel and limestone Inventory, Raw Materials, Gross Plant materials and supplies Other Inventory, Supplies, Gross Other Other Inventory, Gross Total inventories, at average cost Inventory, Net Dpler [Member] Dpler [Member] DPLER [Member] Related Party Transaction [Axis] Related Party Transaction [Axis] Related Party Transaction [Domain] Related Party Transaction [Domain] Insurance Proceeds Received [Member] Insurance Proceeds Received [Member] Insurance Proceeds Received [Member] Charges for health, welfare and benefit plans [Member] Charges for health, welfare and benefit plans [Member] Charges for health, welfare and benefit plans [Member] Related Party [Axis] Related Party [Axis] Related Party [Domain] Related Party [Domain] AES affiliates [Member] Subsidiary of Common Parent [Member] Balance Sheet Location [Axis] Balance Sheet Location [Axis] Balance Sheet Location [Domain] Balance Sheet Location [Domain] Prepaid Expenses and Other Current Assets [Member] Prepaid Expenses and Other Current Assets [Member] Note to DPL Capital Trust II Maturing in September 2031 - 8.125% [Member] Eight Point One Two Five Percentage Of Note To Capital Trust Ii Maturing In September Two Thousand Thirty One [Member] Eight Point One Two Five Percentage Of Note To Capital Trust II Maturing In September Two Thousand Thirty One [Member] Charges for services provided Related Party Transaction, Expenses from Transactions with Related Party Sales to related party Revenue from Related Parties Transactions with other AES affiliates Related Party Transaction, Amounts of Transaction Premiums paid for insurance services provided by MVIC Related Party Transaction, Selling, General and Administrative Expenses from Transactions with Related Party Expense recoveries for services provided to DPLER Related Party Transaction Expense Recoveries Related party expenses, such as employee-related expenses, accounting, information technology, payroll, legal and other administration expenses where the expenses are subsequently charged, at cost, to the related party thereby recovering the expense. Net advance / (payable) to the Service Company Accounts Payable, Related Parties, Current Investment in trust Variable Interest Entity, Nonconsolidated, Carrying Amount, Liabilities Note payable to trust Long-term Debt, Gross Gain on termination of contract Gain (Loss) on Contract Termination Accounts Receivable, Related Parties, Current Accounts Receivable, Related Parties, Current Notes Payable, Related Parties Proceeds from Related Party Debt Debt Instrument, Interest Rate, Stated Percentage Related Party Transaction, Rate Notes Payable, Related Parties Notes Payable, Related Parties Business Segments Segment Reporting Disclosure [Text Block] Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Table] Asset Class [Axis] Asset Class [Axis] Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Asset Types [Domain] Asset Class [Domain] Money Market Funds [Member] Money Market Funds [Member] Equity Securities [Member] Equity Securities [Member] Debt Securities [Member] Debt Securities [Member] Hedge Funds [Member] Hedge Funds [Member] Real Estate Funds [Member] Real Estate Funds [Member] Debt [Member] Debt [Member] Measurement Basis [Axis] Measurement Basis [Axis] Fair Value Measurement [Domain] Fair Value Measurement [Domain] Portion at Fair Value Measurement [Member] Portion at Fair Value Measurement [Member] Cost [Member] Reported Value Measurement [Member] Fair Value [Member] Estimate of Fair Value Measurement [Member] Total Master Trust Assets, Cost Other Investments and Securities, at Cost Total Master Trust Assets, Fair Value Investments, Fair Value Disclosure Total Assets Investments Other Than Derivatives The total of assets that are measured on a recurring basis. Debt, Cost Lines of Credit, Fair Value Disclosure Debt, Fair Value Long-term Debt, Fair Value Fair Value and Cost Of Non-Derivative Instruments Schedule Of Fair Value And Cost Of Non-Derivative Instruments [Table Text Block] Schedule Of Fair Value And Cost Of Non-Derivative Instruments [Table Text Block] Fair Value of Assets and Liabilities Measured on Recurring Basis Schedule of Fair Value, Assets and Liabilities Measured on Recurring Basis [Table Text Block] Fair Value Measurements, Nonrecurring [Table Text Block] Fair Value Measurements, Nonrecurring [Table Text Block] Fair Value Inputs, Assets, Quantitative Information [Table Text Block] Fair Value Inputs, Assets, Quantitative Information [Table Text Block] Fair Value Fair Value Disclosures [Text Block] Stockholders' Equity Note [Abstract] Schedule of Stock by Class [Table] Schedule of Stock by Class [Table] Class of Stock [Line Items] Class of Stock [Line Items] Par value common shares (in USD per share) PUCO merger equity ratio approval (at least) PUCO Merger Equity Ratio Approval PUCO Merger Equity Ratio Approval PUCO Equity Ratio PUCO Equity Ratio Total Common Shareholders' Equity / Total Capitalization PUCO merger, maximum long-term debt allowed Merger Agreement, Long Term Debt, Maximum Merger Agreement, Long Term Debt, Maximum PUCO merger, maximum long-term debt as percent of rate base (percent) Merger Agreement, Long-term Debt as Percentage of Rate Base, Maximum Merger Agreement, Long-term Debt as Percentage of Rate Base, Maximum Pension and Postretirement Benefits Pension and Other Postretirement Benefits Disclosure [Text Block] Derivative [Table] Derivative [Table] Hedging Designation [Axis] Hedging Designation [Axis] Hedging Designation [Domain] Hedging Designation [Domain] Not Designated as Hedging Instrument [Member] Not Designated as Hedging Instrument [Member] Income Statement Location [Axis] Income Statement Location [Axis] Income Statement and Other Comprehensive Income Location [Domain] Income Statement Location [Domain] Regulatory Asset [Member] Regulatory Asset [Member] Regulatory Asset [Member] Revenue [Member] Sales [Member] Purchased Power [Member] Cost of Sales [Member] Derivative Instrument [Axis] Derivative Instrument [Axis] Derivative Contract Type [Domain] Derivative Contract [Domain] Commodity Contract - Heating Oil [Member] Commodity Contract Heating Oil [Member] Forward based contracts to sell or purchase NYMEX Heating Oil Commodity Contract - FTR [Member] Commodity Contract Ftr [Member] Forward based contracts to sell or purchase financial transmission rights with attributes specified by the PJM RTO. Forward Contract Power [Member] Forward Contract Power [Member] Forward Power Contracts negotiated between two parties to purchase and sell a specific quantity of a commodity at a price specified at origination of the contract, with delivery and settlement at a specified future date. Natural Gas [Member] Natural Gas [Member] Change in unrealized gain / (loss) Unrealized Gain Loss on Derivatives, Change The increases (decreases) in the market value of derivative instruments, including options, swaps, futures, and forward contracts, which were included in earnings or deferred on the balance sheet in the period. Realized loss Gain (Loss) on Derivative Instruments, Net, Pretax Derivative, Gain (Loss) on Derivative, Net Derivative, Gain (Loss) on Derivative, Net Consolidation Items [Axis] Consolidation Items [Axis] Consolidation Items [Domain] Consolidation Items [Domain] Operating Segments [Member] Operating Segments [Member] Other [Member] Corporate, Non-Segment [Member] Adjustments and Eliminations [Member] Consolidation, Eliminations [Member] Segments [Axis] Segments [Axis] Segment, Business [Domain] Segments [Domain] Utility [Member] Utility [Member] Utility [Member] Competitive Retail [Member] Competitive Retail [Member] Competitive Retail [Member] External customer revenues External customer revenues External customer revenues Intersegment revenues Related Party Transaction, Other Revenues from Transactions with Related Party Total revenues Electric Revenue, Including Discontinued Operations Electric Revenue, Including Discontinued Operations Fuel Costs Fuel Costs Purchased power Cost of Purchased Power, Including Discontinued Operation Cost of Purchased Power, Including Discontinued Operation Gross margin Gross Profit, Including Discontinued Operation Gross Profit, Including Discontinued Operation Depreciation and amortization Depreciation, Depletion and Amortization, Including Discontinued Operation Depreciation, Depletion and Amortization, Including Discontinued Operation Interest expense Interest and Debt Expense Income tax expense / (benefit) Income Tax Expense (Benefit), Including Discontinued Operation Income Tax Expense (Benefit), Including Discontinued Operation Net income / (loss) from continuing operations Income (Loss) from Continuing Operations Attributable to Parent Discontinued operations, net of tax Income (Loss) from Discontinued Operations, Net of Tax, Attributable to Parent Net income/ (loss) Capital expenditures Property, Plant and Equipment, Additions Total assets Assets Designated as Hedging Instrument [Member] Designated as Hedging Instrument [Member] Purchase of Units Derivative Instruments Financial Transmission Rights Purchase of Units Derivative Instruments Financial Transmission Rights The aggregate notional amount of contracts to purchase financial transmission rights Purchase of Units Derivative Instruments Natural Gas Purchase of Units Derivative Instruments Natural Gas Purchase of Units Derivative Instruments Natural Gas Purchase of Units Derivative Instruments Forward Power Contracts Designated as Cash Flow Hedge Purchase of Units Derivative Instruments Forward Power Contracts Designated as Cash Flow Hedge The aggregate notional amount of contracts to purchase forward power designated as cash flow hedges. Purchase of Units Derivative Instruments Forward Power Contracts Not Designated as Hedged Purchase of Units Derivative Instruments Forward Power Contracts Not Designated as Hedged The aggregate notional amount of contracts to purchase forward power not designated as hedged. Sale of Units Derivative Instruments Financial Transmission Rights Sale of Units Derivative Instruments Financial Transmission Rights Sale of Units Derivative Instruments Financial Transmission Rights Sale of Units Derivative Instruments Natural Gas Sale of Units Derivative Instruments Natural Gas Sale of Units Derivative Instruments Natural Gas Sales of Units Derivative Instruments Forward Power Contracts Designated as Cash Flow Hedge Sales of Units Derivative Instruments Forward Power Contracts Designated as Cash Flow Hedge The aggregate notional amount of contracts to sell forward power designated as cash flow hedges. Sales of Units Derivative Instruments Forward Power Contracts Not Designated as Hedged Sales of Units Derivative Instruments Forward Power Contracts Not Designated as Hedged The aggregate notional amount of contracts to sell forward power not designated as hedged. Derivative, Nonmonetary Notional Amount MWh Derivative, Nonmonetary Notional Amount, Purchase (Sales), Net Net non-monetary notional amount of commodities measured in MWh Disposal Groups, Including Discontinued Operations [Table] Disposal Groups, Including Discontinued Operations [Table] Disposal Group Name [Axis] Disposal Group Name [Axis] Disposal Group Name [Domain] Disposal Group Name [Domain] Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items] Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items] Deposit received on sale of DPLER Deposit, Sale of Business Deposit, Sale of Business Property, plant & equipment, net Disposal Group, Including Discontinued Operation, Property, Plant and Equipment Intangible assets, net Disposal Group, Including Discontinued Operation, Intangible Assets Other assets Disposal Group, Including Discontinued Operation, Other Assets Total assets of the disposal group classified as held for sale in the balance sheets Disposal Group, Including Discontinued Operation, Assets Accounts payable Disposal Group, Including Discontinued Operation, Accounts Payable Other liabilities Disposal Group, Including Discontinued Operation, Other Liabilities Total liabilities of the disposal group classified as held for sale in the balance sheets Disposal Group, Including Discontinued Operation, Liabilities Revenues Disposal Group, Including Discontinued Operation, Revenue Cost of revenues Disposal Group, Including Discontinued Operation, Costs of Goods Sold Operating expenses Disposal Group, Including Discontinued Operation, Operating Expense (Loss) / income from discontinued operations before income taxes Discontinued Operation, Income (Loss) from Discontinued Operation, before Income Tax Gain from disposal of discontinued operations Discontinued Operation, Gain (Loss) from Disposal of Discontinued Operation, before Income Tax Income tax expense / (benefit) for discontinued operations Discontinued Operation, Tax Effect of Discontinued Operation Discontinued operations Cash flows from operating activities for discontinued operations Cash Provided by (Used in) Operating Activities, Discontinued Operations Cash flows from investing activities for discontinued operations Cash Provided by (Used in) Investing Activities, Discontinued Operations Income tax (expense)/benefit on unrealized gains (losses) related to available-for-sale securities Other Comprehensive Income (Loss), Available-for-sale Securities, Tax Income tax (expense) benefit on reclassification to earnings Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI for Sale of Securities, Tax Income tax (expense)/benefit on unrealized gains (losses) related to derivative activity Other Comprehensive Income (Loss), Unrealized Gain (Loss) on Derivatives Arising During Period, Tax Income tax (expense)/benefit on reclassification of earnings related to derivative activity Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI on Derivatives, Tax Income tax (expense)/benefit on reclassification of earnings related to pension and postretirement activity Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI, Pension and Other Postretirement Benefit Plans, for Net Gain (Loss), Tax Statement of Cash Flows [Abstract] Cash flows from operating activities: Net Cash Provided by (Used in) Operating Activities [Abstract] Adjustments to reconcile net income / (loss) to net cash from operating activities: Adjustments to Reconcile Net Income (Loss) to Cash Provided by (Used in) Operating Activities [Abstract] Amortization of debt market value adjustments Amortization of Debt Discount (Premium) Charge for early retirement of debt Gains (Losses) on Extinguishment of Debt Deferred income taxes Deferred Income Tax Expense (Benefit) Gain on sale of business Changes in certain assets and liabilities: Increase (Decrease) in Operating Capital [Abstract] Accounts receivable Increase (Decrease) in Receivables Inventories Increase (Decrease) in Inventories Prepaid taxes Increase (Decrease) in Prepaid Taxes Taxes applicable to subsequent years Increase (Decrease) in Taxes Applicable to Subsequent Years The net change during the reporting period in the aggregate value of capitalized property and other taxes, associated with underlying transactions that are classified as operating activities. Deferred regulatory costs, net Increase (Decrease) in Regulatory Assets and Liabilities Accounts payable Increase (Decrease) in Accounts Payable Accrued taxes payable Increase (Decrease) in Income Taxes Payable Accrued interest payable Increase (Decrease) in Interest Payable, Net Unamortized Investment tax credit Increase (Decrease) in Security Deposits Insurance and claims costs Increase (Decrease) in Self Insurance Reserve Pension, retiree and other benefits Increase (Decrease) in Pension and Postretirement Obligations Other Increase (Decrease) in Other Operating Assets and Liabilities, Net Net cash provided by operating activities Net Cash Provided by (Used in) Operating Activities Cash flows from investing activities: Net Cash Provided by (Used in) Investing Activities [Abstract] Capital expenditures Payments to Acquire Productive Assets Proceeds from sale of business Proceeds from Divestiture of Businesses Insurance proceeds Proceeds from Insurance Settlement, Investing Activities Purchase of intangible assets Payments to Acquire Intangible Assets Increase in restricted cash Increase (Decrease) in Restricted Cash Other investing activities, net Payments for (Proceeds from) Other Investing Activities Net cash used in investing activities Net Cash Provided by (Used in) Investing Activities Cash flows from financing activities: Net Cash Provided by (Used in) Financing Activities [Abstract] Payments of Deferred Finance Costs Payments of Deferred Finance Costs Payments of Deferred Finance Costs Retirement of long-term debt Repayments of Long-term Debt Borrowings from revolving credit facilities Proceeds from Lines of Credit Repayment of borrowings from revolving credit facilities Repayments of Lines of Credit Dividends paid on common stock to parent Payments of Ordinary Dividends, Common Stock Issuance of short-term debt - related party Repayment of short-term debt - related party Repayments of Related Party Debt Dividends paid on preferred stock Payments of Ordinary Dividends, Preferred Stock and Preference Stock Proceeds from (Payments for) Other Financing Activities Proceeds from (Payments for) Other Financing Activities Net cash used in financing activities Net Cash Provided by (Used in) Financing Activities Cash and cash equivalents: Cash and Cash Equivalents, at Carrying Value [Abstract] Net change Cash and Cash Equivalents, Period Increase (Decrease) Balance at beginning of period Cash and Cash Equivalents, at Carrying Value Cash and cash equivalents at end of period Supplemental cash flow information: Supplemental Cash Flow Information [Abstract] Interest paid, net of amounts capitalized Interest Paid, Net Income taxes paid / (refunded), net Proceeds from Income Tax Refunds Income Taxes Paid, Net Income Taxes Paid, Net Non-cash financing and investing activities: Cash Flow, Noncash Investing and Financing Activities Disclosure [Abstract] Accruals for capital expenditures Capital Expenditures Incurred but Not yet Paid Derivative Instruments, Gain (Loss) [Table] Derivative Instruments, Gain (Loss) [Table] Interest Expense [Member] Interest Expense [Member] Interest Rate Contract [Member] Interest Rate Contract [Member] Accumulated Derivative Gain/Loss in AOCI [Roll Forward] Accumulated Derivative Gain/Loss in AOCI [Roll Forward] Accumulated Derivative Gain/Loss in AOCI [Roll Forward] Beginning accumulated derivative gain / (loss) in AOCI Accumulated Other Comprehensive Income (Loss), Cumulative Changes in Net Gain (Loss) from Cash Flow Hedges, Effect Net of Tax Net gains / (losses) associated with current period hedging transactions Derivative Instruments, Gain (Loss) Recognized in Other Comprehensive Income (Loss), Effective Portion, Net Net gains losses reclassified to earnings Derivative Instruments, Gain (Loss) Reclassified from Accumulated OCI into Income, Effective Portion, Net Ending accumulated derivative gain / (loss) in AOCI Portion expected to be reclassified to earnings in the next twelve months Interest Rate Cash Flow Hedge Gain (Loss) to be Reclassified During Next 12 Months, Net Maximum length of time that we are hedging our exposure to variability in future cash flows related to forecasted transactions (in months) Maximum Length of Time Hedged in Cash Flow Hedge ASSETS Assets [Abstract] Current assets: Assets, Current [Abstract] Cash and cash equivalents Restricted cash Restricted Cash and Cash Equivalents, Current Accounts receivable, net Inventories Taxes applicable to subsequent years Taxes Applicable to Subsequent Years Carrying amount as of the balance sheet date of capitalized property and other taxes which will be charged against earnings within one year or the normal operating cycle, if longer. Regulatory assets, current Regulatory Assets, Current Other prepayments and current assets Other Assets, Current Disposal Group, Including Discontinued Operation, Other Assets, Current Disposal Group, Including Discontinued Operation, Other Assets, Current Total current assets Assets, Current Property, plant & equipment: Property, Plant and Equipment, Net [Abstract] Property, plant & equipment Property, Plant and Equipment, Gross Less: Accumulated depreciation and amortization Accumulated Depreciation, Depletion and Amortization, Property, Plant, and Equipment Property, plant and equipment, net of depreciation Property Plant And Equipment, Net of Depreciation Total net property plant and equipment which was in service as of the balance sheet date. Construction work in process Construction in Progress, Gross Total net property, plant & equipment Other non-current assets: Other Assets, Noncurrent [Abstract] Regulatory assets, non-current Regulatory Assets, Noncurrent Intangible assets, net of amortization Intangible Assets, Net (Excluding Goodwill) Other deferred assets Other Assets, Noncurrent Total other non-current assets Other Noncurrent Assets, Excluding Property Plant and Equipment, Net This element represents sum of the carrying amounts as of the balance sheet date of all assets excluding property plant equipment that are expected to be realized in cash, sold or consumed after one year or beyond the normal operating cycle, if longer. Total assets LIABILITIES AND SHAREHOLDER'S EQUITY Liabilities and Equity [Abstract] Current liabilities: Liabilities, Current [Abstract] Current portion of long-term debt Debt, Current Short-term debt Short-term Debt Accounts payable Accounts Payable, Current Accrued taxes Taxes Payable, Current Accrued interest Interest Payable, Current Security deposits Customer Deposits, Current Regulatory liabilities, current Regulatory Liability, Current Insurance and claims costs Self Insurance Reserve, Current Other current liabilities Other Liabilities, Current Deposit, Sale of Business Disposal Group, Including Discontinued Operation, Liabilities, Current Disposal Group, Including Discontinued Operation, Liabilities, Current Advance on contract termination Advance Payments Netted Against Claim Receivable Total current liabilities Liabilities, Current Non-current liabilities: Liabilities, Noncurrent [Abstract] Long-term debt Long-term Debt, Excluding Current Maturities Deferred taxes Deferred Tax Liabilities, Net, Noncurrent Taxes payable Taxes Payable Regulatory liabilities, non-current Regulatory Liability, Noncurrent Pension, retiree and other benefits Pension and Other Postretirement Defined Benefit Plans, Liabilities, Noncurrent Unamortized investment tax credit Accumulated Deferred Investment Tax Credit Other deferred credits Other Liabilities, Noncurrent Total non-current liabilities Liabilities, Noncurrent Redeemable preferred stock of subsidiary Redeemable Noncontrolling Interest, Equity, Carrying Amount Commitments and contingencies Commitments and Contingencies Common shareholder's equity: Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest [Abstract] Common stock Common Stock, Value, Issued Other paid-in capital Additional Paid in Capital, Common Stock Accumulated other comprehensive income Retained earnings/ (deficit) Retained Earnings (Accumulated Deficit) Total common shareholder's equity Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest Total liabilities and shareholder's equity Liabilities and Equity Supplemental Financial Information Supplemental Balance Sheet Disclosures [Text Block] Overview and Summary of Significant Accounting Policies Significant Accounting Policies [Text Block] Derivative Instruments and Hedging Activities Disclosures [Table] Derivative Instruments and Hedging Activities Disclosures [Table] Derivative Instruments and Hedging Activities Disclosures [Line Items] Derivative Instruments and Hedging Activities Disclosures [Line Items] Schedule of Notional Amounts of Outstanding Derivative Positions Schedule of Notional Amounts of Outstanding Derivative Positions [Table Text Block] Gains or Losses Recognized in AOCI for the Cash Flow Hedges Schedule of Derivative Instruments, Effect on Other Comprehensive Income (Loss) [Table Text Block] Schedule of Other Derivatives Not Designated as Hedging Instruments, Statements of Financial Performance and Financial Position, Location Schedule of Other Derivatives Not Designated as Hedging Instruments, Statements of Financial Performance and Financial Position, Location [Table Text Block] Schedule of Derivative Instruments in Statement of Financial Position, Fair Value Schedule of Derivative Instruments in Statement of Financial Position, Fair Value [Table Text Block] Income Statement [Abstract] Revenues Electric Revenue Cost of revenues: Cost of Revenue [Abstract] Fuel Purchased power Cost of Purchased Power Total cost of revenues Cost of Goods Sold, Electric Gross margin Gross Profit Operating expenses: Operating Expenses [Abstract] Operation and maintenance Utilities Operating Expense, Maintenance and Operations Depreciation and amortization Depreciation, Depletion and Amortization General taxes Taxes, Miscellaneous Gain on termination of contract Other Gain (Loss) on Sale of Assets and Asset Impairment Charges Total operating expenses Operating Expenses Operating income / (loss) Operating Income (Loss) Other income / (expense), net Nonoperating Income (Expense) [Abstract] Investment income Investment Income, Net Interest expense Charge for early retirement of debt Other expense Other Nonoperating Income (Expense) Total other expense, net Nonoperating Income (Expense) Earnings / (loss) from continuing operations before income taxes Income (Loss) from Continuing Operations before Equity Method Investments, Income Taxes, Extraordinary Items, Noncontrolling Interest Income tax expense / (benefit) from continuing operations Income Tax Expense (Benefit) Net income / (loss) from continuing operations Income / (loss) from discontinued operations Net income / (loss) Dividends on preferred stock Dividends, Preferred Stock Income / (loss) attributable to common stock Net Income (Loss) Available to Common Stockholders, Basic First Mortgage Bonds Maturing in September 2016 - 1.875% [Member] One Point Nine Percentage Of First Mortgage Bonds Maturing September Two Thousand Sixteen [Member] One Point Nine Percentage Of First Mortgage Bonds Maturing September Two Thousand Sixteen [Member] Pollution Control Series Maturing in September 2036 - 4.80% [Member] Four Point Eight Zero Percentage Of Pollution Control Series Maturing In September Two Thousand Thirty Six [Member] Four Point Eight Zero Percentage Of Pollution Control Series Maturing In September Two Thousand Thirty Six [Member] Pollution Control Series Maturing in August 2020 - 1.13% - 1.14% [Member] Variable Rate Notes Backed by Term Loan and First Mortgage Bonds [Member] Variable Rate Notes Backed by Term Loan and First Mortgage Bonds [Member] Zero Point Two Three To Zero Point Two Nine And Zero Point One Six To Zero Point Three Six Percentage Of Pollution Control Series Maturing In November Two Thousand Forty [Member] Zero Point Two Three To Zero Point Two Nine And Zero Point One Six To Zero Point Three Six Percentage Of Pollution Control Series Maturing In November Two Thousand Forty [Member] Zero Point Two Three To Zero Point Two Nine And Zero Point One Six to Zero Point Three Six Percentage Of Pollution Control Series Maturing In November Two Thousand Forty [Member] U.S. Government note maturing in February 2061 - 4.20% [Member] Four Point Two Zero Percentage Of U S Government Note Maturing In February Two Thousand Sixty One [Member] Four Point Two Zero Percentage Of U S Government Note Maturing In February Two Thousand Sixty One [Member] Bank term loan due in July 2020 - rates from: 2.44% - 2.45% [Member] Bank Term Loan Maturing July 2020 [Member] Bank Term Loan Maturing July 2020 [Member] Senior unsecured due in October 2016 - 6.5% [Member] Five Year Senior Unsecured Notes At650 Maturing On October152016 [Member] Five Year Senior Unsecured Notes at 6.50% maturing on October 15, 2016 [Member] Senior unsecured due in October 2019 - 6.75% [Member] Senior Unsecured Notes At6.80 Maturing On October2019 [Member] Senior Unsecured notes maturing October 2019 at 6.8% Senior unsecured due in October 2021 - 7.25% [Member] Ten Year Senior Unsecured Notes At725 Maturing At October152021 [Member] Ten Year Senior Unsecured Notes at 7.25% maturing at October 15, 2021 [Member] Long-term debt, gross Unamortized deferred finance costs Deferred Finance Costs, Net, Including Acquisition Adjustments Deferred Finance Costs, Net, Including Acquisition Adjustments Unamortized deferred finance costs Deferred Finance Costs, Net Unamortized debt discount and premiums, net Debt Instrument, Unamortized Discount (Premium), Net Unamortized debt discount Debt Instrument, Unamortized Discount Total long-term debt at subsidiary Total Long-term Debt At Subsidiary With Purchase Accounting Adjustments Total Long-term Debt At Subsidiary With Purchase Accounting Adjustments Total long-term debt Long-term Debt Less: current portion Long-term Debt, Current Maturities Debt instrument maturity year Debt Instrument, Maturity Date Range, End Debt instrument interest percentage Debt Instrument, Interest Rate, Stated Percentage Debt instrument interest percentage minimum Debt Instrument, Interest Rate, Stated Percentage Rate Range, Minimum Debt instrument interest percentage maximum Debt Instrument, Interest Rate, Stated Percentage Rate Range, Maximum Hedging Relationship [Axis] Hedging Relationship [Axis] Hedging Relationship [Domain] Hedging Relationship [Domain] Cash Flow Hedging [Member] Cash Flow Hedging [Member] Fair Value Hedging [Member] Fair Value Hedging [Member] Natural Gas Futures [Member] Natural Gas Futures [Member] Natural Gas Futures [Member] Fair Values of Derivative Position [Axis] Fair Values of Derivative Position [Axis] Fair Values of Derivative Position [Axis] Fair Values of Derivative Position [Domain] Fair Values Of Derivative Position [Domain] Fair Values of Derivative Position [Domain] Short-term Derivative Positions [Member] Short Term Derivative Position [Member] Fair value of forward contracts in an asset or liability position maturing in 12 months or less. Long-term Derivative Positions [Member] Long Term Derivative Position [Member] Fair value of forward contracts in an asset or liability position maturing in more than 12 months. Total Assets [Member] Derivative Financial Instruments, Assets [Member] Total Liabilities [Member] Derivative Financial Instruments, Liabilities [Member] Other Prepayments and Current Assets [Member] Other Prepayments And Current Asset [Member] Current assets not separately presented elsewhere in the balance sheet. Current assets are expected to be realized or consumed within one year (or the normal operating cycle, if longer). Other Deferred Asset [Member] Other Deferred Asset [Member] Noncurrent assets not separately disclosed in the balance sheet due to materiality considerations. Noncurrent assets are expected to be realized or consumed after one year (or the normal operating cycle, if longer). Other Current Liabilities [Member] Other Current Liabilities [Member] Other Deferred Credit [Member] Other Deferred Credit [Member] Noncurrent obligations not separately disclosed in the balance sheet due to materiality considerations. Noncurrent liabilities are expected to be paid after one year (or the normal operating cycle, if longer). Derivative Asset, Fair Value Derivative Asset, Fair Value, Gross Asset Derivative, Collateral, Obligation to Return Securities Derivative, Collateral, Obligation to Return Securities Derivative, Collateral, Obligation to Return Cash Derivative, Collateral, Obligation to Return Cash Derivative Asset, Fair Value, Amount Offset Against Collateral Derivative Asset, Fair Value, Amount Offset Against Collateral Derivative Liability, Fair Value Derivative, Collateral, Right to Reclaim Securities Derivative, Collateral, Right to Reclaim Securities Derivative, Collateral, Right to Reclaim Cash Derivative, Collateral, Right to Reclaim Cash Liability position offset by the asset position of counterparties with master netting agreements Long-term Debt Debt Disclosure [Text Block] Current Portion - Long-term Debt Schedule of Short-term Debt [Table Text Block] Income Taxes Income Tax Disclosure [Text Block] Revolving Credit Agreement and Standby Letters of Credit [Member] Revolving Credit Agreement and Standby Letters of Credit [Member] Revolving Credit Agreement and Standby Letters of Credit [Member] Revolving Credit Agreement and Term Loan [Member] DPL Revolving Credit Agreement and Term Loan Maturing July 2020 [Member] DPL Revolving Credit Agreement and Term Loan Maturing July 2020 [Member] Debt called/redeemed Extinguishment of Debt, Amount Term loan outstanding Basis points on Treasury bond yield (percent) Debt Instrument, Basis Spread on Variable Rate Retirement of long-term debt Number of financial covenants Debt Instrument, Number of Financial Covenants Debt Instrument, Number of Financial Covenants Number of prior quarters included in EBITDA to interest calculation Debt Instrument, Debt Covenant, EBITDA to Interest Calculation, Number of Quarters Debt Instrument, Debt Covenant, EBITDA to Interest Calculation, Number of Quarters Number of prior quarters included in debt to EBITDA ratio Debt Instrument, Debt Covenant, Debt to EBITDA Ratio, Number of Quarters Debt Instrument, Debt Covenant, Debt to EBITDA Ratio, Number of Quarters Schedule of Related Party Transactions Schedule of Related Party Transactions [Table Text Block] 2016 Defined Benefit Plan, Expected Future Benefit Payments, Next Twelve Months 2017 Defined Benefit Plan, Expected Future Benefit Payments, Year Two 2018 Defined Benefit Plan, Expected Future Benefit Payments, Year Three 2019 Defined Benefit Plan, Expected Future Benefit Payments, Year Four 2020 Defined Benefit Plan, Expected Future Benefit Payments, Year Five 2021 - 2025 Defined Benefit Plan, Expected Future Benefit Payments, Five Fiscal Years Thereafter Reclassification out of Accumulated Other Comprehensive Income [Table] Reclassification out of Accumulated Other Comprehensive Income [Table] Amortization of defined benefit pension items [Member] Reclassification out of Accumulated Other Comprehensive Income [Axis] Reclassification out of Accumulated Other Comprehensive Income [Axis] Reclassification out of Accumulated Other Comprehensive Income [Domain] Reclassification out of Accumulated Other Comprehensive Income [Domain] Reclassification out of Accumulated Other Comprehensive Income [Member] Reclassification out of Accumulated Other Comprehensive Income [Member] Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items] Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items] Other income Tax expense Revenue Purchased power Operating Expenses Total before income taxes Income (Loss) from Continuing Operations before Income Taxes, Extraordinary Items, Noncontrolling Interest Derivative Instruments and Hedging Activities Derivative Instruments and Hedging Activities Disclosure [Text Block] Fixed-asset Impairment (Narrative) [Abstract] Fixed-asset Impairment (Narrative) [Abstract] Schedule of Net Periodic Benefit Cost / (Income) Schedule of Net Periodic Benefit Cost / (Income) [Table Text Block] Schedule of Net Periodic Benefit Cost / (Income) [Table Text Block] Estimated Future Benefit Payments and Medicare Part D Reimbursements Schedule of Expected Benefit Payments [Table Text Block] Shareholder's Equity Stockholders' Equity Note Disclosure [Text Block] Level 1 [Member] Total Derivative Assets Derivative Asset Total Assets Assets, Fair Value Disclosure Total Derivative Liabilities Derivative Liability Debt Debt Instrument, Fair Value Disclosure Total Liabilities Financial and Nonfinancial Liabilities, Fair Value Disclosure Summary of Balance Sheet and Profit and Loss Information for Discontinued Operations Disposal Groups, Including Discontinued Operations [Table Text Block]