v3.24.0.1
Leases (Details) - USD ($)
$ in Millions
 1 Months Ended 12 Months Ended
Feb. 26, 2024
Jan. 31, 2024
Dec. 31, 2023
Dec. 31, 2022
Dec. 31, 2021
Lease Rental Costs          
Operating Lease, Cost     $ 149.9 $ 157.5 $ 275.3
Finance Lease Right-of-Use Asset Amortization     69.1 205.5 74.7
Interest Expense on Finance Leases     11.9 13.4 14.4
Total Lease Rental Costs [1]     $ 230.9 $ 376.4 364.4
Supplemental Information Related to Leases          
Weighted-Average Remaining Lease Term, Operating Leases     12 years 6 months 29 days 12 years 8 months 8 days  
Weighted Average Remaining Lease Term, Finance Leases     4 years 7 months 17 days 4 years 7 months 9 days  
Weighted Average Discount Rate, Operating Leases     3.73% 3.54%  
Weighted Average Discount Rate, Finance Leases     6.19% 5.76%  
Operating Cash Flows Used for Operating Leases     $ 146.8 $ 155.1  
Operating Cash Flows Used for Finance Leases     11.9 13.6  
Financing Cash Flows Used for Finance Leases     68.3 309.5 64.0
Non-cash Acquisitions Under Operating Leases     99.8 191.4  
Property, Plant and Equipment and Other Related Obligations Under Finance Leases          
Generation     24,329.5 25,834.2  
Other Property, Plant and Equipment     6,484.9 5,971.8  
Total Property, Plant and Equipment     101,246.4 97,021.4  
Accumulated Amortization     24,553.0 23,682.3  
Net Property, Plant and Equipment Under Finance Leases     204.5 212.7  
Other Liabilities, Noncurrent     545.8 607.3  
Finance Lease Liability Due Within One Year     1,251.1 1,278.2  
Total Obligations Under Finance Leases     205.6 225.7  
Operating Lease Asset and Related Obligations          
Operating Lease Assets     620.2 645.5  
Operating Lease Noncurrent Liability     519.4 552.5  
Operating Lease Liability Due Within One Year     115.7 113.6  
Estimated Present Value of Future Minimum Lease Payments on Operating Leases     635.1 666.1  
Finance Lease Liabilities Rolling Future Minimum Lease Payments          
Year 1     76.8    
Year 2     48.6    
Year 3     33.0    
Year 4     26.2    
Year 5     19.2    
Finance Leases, Later Years     35.4    
Finance Leases, Total Future Minimum Lease Payments     239.2    
Imputed Interest on Finance Leases     33.6    
Total Obligations Under Finance Leases     205.6 225.7  
Operating Lease Liabilities Rolling Future Minimum Lease Payments          
Year 1     141.6    
Year 2     103.3    
Year 3     92.0    
Year 4     82.6    
Year 5     67.4    
Operating Leases, Later Years     327.6    
Operating Leases, Total Future Minimum Lease Payments     814.5    
Imputed Interest on Operating Leases     179.4    
Estimated Present Value of Future Minimum Lease Payments on Operating Leases     635.1 666.1  
Maximum Potential Loss          
Max Potential Loss on Master Lease Agreements     45.3    
Leases (Textuals)          
Repayments of Long-term Debt     2,196.1 2,345.4 2,989.3
Finance Lease Assets [Member]          
Property, Plant and Equipment and Other Related Obligations Under Finance Leases          
Generation     120.1 120.9  
Other Property, Plant and Equipment     305.9 321.4  
Total Property, Plant and Equipment     426.0 442.3  
Accumulated Amortization     221.5 229.6  
Finance Lease Liabilities [Member]          
Property, Plant and Equipment and Other Related Obligations Under Finance Leases          
Other Liabilities, Noncurrent     139.9 168.4  
Finance Lease Liability Due Within One Year     65.7 57.3  
Operating Lease Assets [Member]          
Operating Lease Asset and Related Obligations          
Operating Lease Assets     620.2 645.5  
AEP Texas Inc. [Member]          
Lease Rental Costs          
Operating Lease, Cost     34.0 18.4 18.4
Finance Lease Right-of-Use Asset Amortization     7.4 6.8 6.7
Interest Expense on Finance Leases     1.4 1.3 1.4
Total Lease Rental Costs [1]     $ 42.8 $ 26.5 26.5
Supplemental Information Related to Leases          
Weighted-Average Remaining Lease Term, Operating Leases     3 years 11 months 26 days 4 years 3 months 29 days  
Weighted Average Remaining Lease Term, Finance Leases     5 years 1 month 17 days 5 years 4 months 20 days  
Weighted Average Discount Rate, Operating Leases     4.23% 4.15%  
Weighted Average Discount Rate, Finance Leases     5.27% 4.75%  
Operating Cash Flows Used for Operating Leases     $ 33.6 $ 18.3  
Operating Cash Flows Used for Finance Leases     1.4 1.3  
Financing Cash Flows Used for Finance Leases     7.4 6.8 6.7
Non-cash Acquisitions Under Operating Leases     12.4 36.7  
Property, Plant and Equipment and Other Related Obligations Under Finance Leases          
Other Property, Plant and Equipment     1,145.9 1,022.8  
Total Property, Plant and Equipment     14,661.9 13,442.3  
Accumulated Amortization     1,887.9 1,760.7  
Net Property, Plant and Equipment Under Finance Leases     27.6 30.1  
Other Liabilities, Noncurrent     111.3 93.2  
Finance Lease Liability Due Within One Year     152.7 130.7  
Total Obligations Under Finance Leases     27.6 30.1  
Operating Lease Asset and Related Obligations          
Operating Lease Noncurrent Liability     50.9 67.8  
Operating Lease Liability Due Within One Year     28.7 28.6  
Estimated Present Value of Future Minimum Lease Payments on Operating Leases     79.6 96.4  
Finance Lease Liabilities Rolling Future Minimum Lease Payments          
Year 1     8.3    
Year 2     6.6    
Year 3     5.1    
Year 4     4.0    
Year 5     2.8    
Finance Leases, Later Years     5.1    
Finance Leases, Total Future Minimum Lease Payments     31.9    
Imputed Interest on Finance Leases     4.3    
Total Obligations Under Finance Leases     27.6 30.1  
Operating Lease Liabilities Rolling Future Minimum Lease Payments          
Year 1     32.1    
Year 2     15.7    
Year 3     13.3    
Year 4     10.7    
Year 5     7.8    
Operating Leases, Later Years     8.1    
Operating Leases, Total Future Minimum Lease Payments     87.7    
Imputed Interest on Operating Leases     8.1    
Estimated Present Value of Future Minimum Lease Payments on Operating Leases     79.6 96.4  
Maximum Potential Loss          
Max Potential Loss on Master Lease Agreements     10.9    
Leases (Textuals)          
Repayments of Long-term Debt     278.5 716.0 88.7
AEP Texas Inc. [Member] | Finance Lease Assets [Member]          
Property, Plant and Equipment and Other Related Obligations Under Finance Leases          
Generation     0.0 0.0  
Other Property, Plant and Equipment     53.9 53.7  
Total Property, Plant and Equipment     53.9 53.7  
Accumulated Amortization     26.3 23.6  
AEP Texas Inc. [Member] | Finance Lease Liabilities [Member]          
Property, Plant and Equipment and Other Related Obligations Under Finance Leases          
Other Liabilities, Noncurrent     20.6 23.1  
Finance Lease Liability Due Within One Year     7.0 7.0  
AEP Texas Inc. [Member] | Operating Lease Assets [Member]          
Operating Lease Asset and Related Obligations          
Operating Lease Assets     77.6 94.7  
AEP Transmission Co [Member]          
Lease Rental Costs          
Operating Lease, Cost     1.3 1.1 1.7
Finance Lease Right-of-Use Asset Amortization     0.0 0.0 0.0
Interest Expense on Finance Leases     0.0 0.0 0.0
Total Lease Rental Costs [1]     $ 1.3 $ 1.1 1.7
Supplemental Information Related to Leases          
Weighted-Average Remaining Lease Term, Operating Leases     2 years 9 months 3 days 2 years 18 days  
Weighted Average Remaining Lease Term, Finance Leases     0 years 0 years  
Weighted Average Discount Rate, Operating Leases     3.61% 1.96%  
Weighted Average Discount Rate, Finance Leases     0.00% 0.00%  
Operating Cash Flows Used for Operating Leases     $ 1.3 $ 1.0  
Operating Cash Flows Used for Finance Leases     0.0 0.0  
Financing Cash Flows Used for Finance Leases     0.0 0.0  
Non-cash Acquisitions Under Operating Leases     1.2 1.7  
Property, Plant and Equipment and Other Related Obligations Under Finance Leases          
Other Property, Plant and Equipment     501.4 476.8  
Total Property, Plant and Equipment     15,789.0 14,366.9  
Accumulated Amortization     1,291.3 1,027.0  
Net Property, Plant and Equipment Under Finance Leases     0.0 0.0  
Other Liabilities, Noncurrent     200.9 69.1  
Finance Lease Liability Due Within One Year     24.7 8.3  
Total Obligations Under Finance Leases     0.0 0.0  
Operating Lease Asset and Related Obligations          
Operating Lease Noncurrent Liability     1.4 1.5  
Operating Lease Liability Due Within One Year     1.3 1.3  
Estimated Present Value of Future Minimum Lease Payments on Operating Leases     2.7 2.8  
Finance Lease Liabilities Rolling Future Minimum Lease Payments          
Year 1     0.0    
Year 2     0.0    
Year 3     0.0    
Year 4     0.0    
Year 5     0.0    
Finance Leases, Later Years     0.0    
Finance Leases, Total Future Minimum Lease Payments     0.0    
Imputed Interest on Finance Leases     0.0    
Total Obligations Under Finance Leases     0.0 0.0  
Operating Lease Liabilities Rolling Future Minimum Lease Payments          
Year 1     1.4    
Year 2     0.7    
Year 3     0.4    
Year 4     0.2    
Year 5     0.1    
Operating Leases, Later Years     0.0    
Operating Leases, Total Future Minimum Lease Payments     2.8    
Imputed Interest on Operating Leases     0.1    
Estimated Present Value of Future Minimum Lease Payments on Operating Leases     2.7 2.8  
Leases (Textuals)          
Repayments of Long-term Debt     60.0 104.0 50.0
AEP Transmission Co [Member] | Finance Lease Assets [Member]          
Property, Plant and Equipment and Other Related Obligations Under Finance Leases          
Generation     0.0 0.0  
Other Property, Plant and Equipment     0.0 0.0  
Total Property, Plant and Equipment     0.0 0.0  
Accumulated Amortization     0.0 0.0  
AEP Transmission Co [Member] | Finance Lease Liabilities [Member]          
Property, Plant and Equipment and Other Related Obligations Under Finance Leases          
Other Liabilities, Noncurrent     0.0 0.0  
Finance Lease Liability Due Within One Year     0.0 0.0  
AEP Transmission Co [Member] | Operating Lease Assets [Member]          
Operating Lease Asset and Related Obligations          
Operating Lease Assets     2.6 2.7  
Appalachian Power Co [Member]          
Lease Rental Costs          
Operating Lease, Cost     18.5 17.9 19.3
Finance Lease Right-of-Use Asset Amortization     8.3 7.9 7.7
Interest Expense on Finance Leases     1.8 2.0 2.4
Total Lease Rental Costs [1]     $ 28.6 $ 27.8 29.4
Supplemental Information Related to Leases          
Weighted-Average Remaining Lease Term, Operating Leases     6 years 3 days 5 years 3 months 14 days  
Weighted Average Remaining Lease Term, Finance Leases     4 years 1 month 28 days 4 years 3 months  
Weighted Average Discount Rate, Operating Leases     3.50% 3.61%  
Weighted Average Discount Rate, Finance Leases     7.04% 7.09%  
Operating Cash Flows Used for Operating Leases     $ 18.3 $ 17.9  
Operating Cash Flows Used for Finance Leases     1.8 2.0  
Financing Cash Flows Used for Finance Leases     8.3 7.9 7.7
Non-cash Acquisitions Under Operating Leases     15.7 23.1  
Property, Plant and Equipment and Other Related Obligations Under Finance Leases          
Generation     7,041.3 6,776.8  
Other Property, Plant and Equipment     981.3 883.3  
Total Property, Plant and Equipment     18,620.2 17,781.2  
Accumulated Amortization     5,688.7 5,402.0  
Net Property, Plant and Equipment Under Finance Leases     26.0 29.3  
Other Liabilities, Noncurrent     70.9 49.6  
Finance Lease Liability Due Within One Year     193.6 171.2  
Total Obligations Under Finance Leases     26.0 29.3  
Operating Lease Asset and Related Obligations          
Operating Lease Assets     73.7 73.6  
Operating Lease Noncurrent Liability     59.8 59.1  
Operating Lease Liability Due Within One Year     14.6 15.0  
Estimated Present Value of Future Minimum Lease Payments on Operating Leases     74.4 74.1  
Finance Lease Liabilities Rolling Future Minimum Lease Payments          
Year 1     9.9    
Year 2     8.5    
Year 3     3.5    
Year 4     2.3    
Year 5     1.9    
Finance Leases, Later Years     3.4    
Finance Leases, Total Future Minimum Lease Payments     29.5    
Imputed Interest on Finance Leases     3.5    
Total Obligations Under Finance Leases     26.0 29.3  
Operating Lease Liabilities Rolling Future Minimum Lease Payments          
Year 1     17.8    
Year 2     14.8    
Year 3     13.3    
Year 4     12.1    
Year 5     10.0    
Operating Leases, Later Years     16.8    
Operating Leases, Total Future Minimum Lease Payments     84.8    
Imputed Interest on Operating Leases     10.4    
Estimated Present Value of Future Minimum Lease Payments on Operating Leases     74.4 74.1  
Maximum Potential Loss          
Max Potential Loss on Master Lease Agreements     5.8    
Leases (Textuals)          
Repayments of Long-term Debt     26.6 230.4 393.0
Appalachian Power Co [Member] | Finance Lease Assets [Member]          
Property, Plant and Equipment and Other Related Obligations Under Finance Leases          
Generation     41.0 41.1  
Other Property, Plant and Equipment     22.1 20.1  
Total Property, Plant and Equipment     63.1 61.2  
Accumulated Amortization     37.1 31.9  
Appalachian Power Co [Member] | Finance Lease Liabilities [Member]          
Property, Plant and Equipment and Other Related Obligations Under Finance Leases          
Other Liabilities, Noncurrent     17.8 21.6  
Finance Lease Liability Due Within One Year     8.2 7.7  
Appalachian Power Co [Member] | Operating Lease Assets [Member]          
Operating Lease Asset and Related Obligations          
Operating Lease Assets     73.7 73.6  
Indiana Michigan Power Co [Member]          
Lease Rental Costs          
Operating Lease, Cost     19.6 29.5 90.2
Finance Lease Right-of-Use Asset Amortization     7.3 78.7 12.9
Interest Expense on Finance Leases     2.5 3.1 3.0
Total Lease Rental Costs [1]     $ 29.4 $ 111.3 106.1
Supplemental Information Related to Leases          
Weighted-Average Remaining Lease Term, Operating Leases     4 years 6 months 10 days 5 years 9 months 14 days  
Weighted Average Remaining Lease Term, Finance Leases     4 years 11 months 12 days 4 years 9 months 3 days  
Weighted Average Discount Rate, Operating Leases     3.89% 3.62%  
Weighted Average Discount Rate, Finance Leases     8.62% 8.99%  
Operating Cash Flows Used for Operating Leases     $ 19.5 $ 29.7  
Operating Cash Flows Used for Finance Leases     2.5 3.2  
Financing Cash Flows Used for Finance Leases     7.4 130.7 6.8
Non-cash Acquisitions Under Operating Leases     7.9 19.1  
Property, Plant and Equipment and Other Related Obligations Under Finance Leases          
Generation     5,646.8 5,585.1  
Other Property, Plant and Equipment     898.5 839.3  
Total Property, Plant and Equipment     12,007.4 11,544.3  
Accumulated Amortization     4,378.4 4,132.8  
Net Property, Plant and Equipment Under Finance Leases     31.5 33.8  
Other Liabilities, Noncurrent     57.7 58.8  
Finance Lease Liability Due Within One Year     91.9 105.8  
Total Obligations Under Finance Leases     31.5 34.0  
Operating Lease Asset and Related Obligations          
Operating Lease Assets     53.8 64.3  
Operating Lease Noncurrent Liability     37.7 48.9  
Operating Lease Liability Due Within One Year     16.8 16.0  
Estimated Present Value of Future Minimum Lease Payments on Operating Leases     54.5 64.9  
Finance Lease Liabilities Rolling Future Minimum Lease Payments          
Year 1     12.8    
Year 2     7.2    
Year 3     4.5    
Year 4     4.0    
Year 5     3.3    
Finance Leases, Later Years     7.3    
Finance Leases, Total Future Minimum Lease Payments     39.1    
Imputed Interest on Finance Leases     7.6    
Total Obligations Under Finance Leases     31.5 34.0  
Operating Lease Liabilities Rolling Future Minimum Lease Payments          
Year 1     18.9    
Year 2     10.6    
Year 3     9.7    
Year 4     8.9    
Year 5     7.0    
Operating Leases, Later Years     4.8    
Operating Leases, Total Future Minimum Lease Payments     59.9    
Imputed Interest on Operating Leases     5.4    
Estimated Present Value of Future Minimum Lease Payments on Operating Leases     54.5 64.9  
Maximum Potential Loss          
Max Potential Loss on Master Lease Agreements     4.1    
Leases (Textuals)          
Repayments of Long-term Debt     343.3 83.4 383.5
Indiana Michigan Power Co [Member] | Notes Payable, Other Payables [Member] | Subsequent Event [Member]          
Leases (Textuals)          
Repayments of Long-term Debt $ 8.0 $ 8.0      
Indiana Michigan Power Co [Member] | Finance Lease Assets [Member]          
Property, Plant and Equipment and Other Related Obligations Under Finance Leases          
Generation     28.2 28.0  
Other Property, Plant and Equipment     42.3 40.6  
Total Property, Plant and Equipment     70.5 68.6  
Accumulated Amortization     39.0 34.8  
Indiana Michigan Power Co [Member] | Finance Lease Liabilities [Member]          
Property, Plant and Equipment and Other Related Obligations Under Finance Leases          
Other Liabilities, Noncurrent     20.8 27.1  
Finance Lease Liability Due Within One Year     10.7 6.9  
Indiana Michigan Power Co [Member] | Operating Lease Assets [Member]          
Operating Lease Asset and Related Obligations          
Operating Lease Assets     53.8 64.3  
Ohio Power Co [Member]          
Lease Rental Costs          
Operating Lease, Cost     17.3 16.9 19.0
Finance Lease Right-of-Use Asset Amortization     5.0 4.9 4.9
Interest Expense on Finance Leases     0.9 0.8 0.8
Total Lease Rental Costs [1]     $ 23.2 $ 22.6 24.7
Supplemental Information Related to Leases          
Weighted-Average Remaining Lease Term, Operating Leases     5 years 4 months 9 days 5 years 11 months 23 days  
Weighted Average Remaining Lease Term, Finance Leases     4 years 11 months 19 days 5 years 3 months 7 days  
Weighted Average Discount Rate, Operating Leases     3.93% 3.73%  
Weighted Average Discount Rate, Finance Leases     5.32% 4.53%  
Operating Cash Flows Used for Operating Leases     $ 17.0 $ 17.5  
Operating Cash Flows Used for Finance Leases     0.9 0.8  
Financing Cash Flows Used for Finance Leases     5.0 4.9 4.9
Non-cash Acquisitions Under Operating Leases     10.2 8.4  
Property, Plant and Equipment and Other Related Obligations Under Finance Leases          
Other Property, Plant and Equipment     1,125.0 1,051.4  
Total Property, Plant and Equipment     12,013.5 11,174.6  
Accumulated Amortization     2,713.6 2,565.3  
Net Property, Plant and Equipment Under Finance Leases     18.2 18.9  
Other Liabilities, Noncurrent     34.4 66.0  
Finance Lease Liability Due Within One Year     183.3 154.2  
Total Obligations Under Finance Leases     18.2 18.9  
Operating Lease Asset and Related Obligations          
Operating Lease Assets     69.9 73.8  
Operating Lease Noncurrent Liability     56.7 60.3  
Operating Lease Liability Due Within One Year     13.5 13.5  
Estimated Present Value of Future Minimum Lease Payments on Operating Leases     70.2 73.8  
Finance Lease Liabilities Rolling Future Minimum Lease Payments          
Year 1     5.8    
Year 2     4.3    
Year 3     3.1    
Year 4     2.5    
Year 5     2.0    
Finance Leases, Later Years     3.2    
Finance Leases, Total Future Minimum Lease Payments     20.9    
Imputed Interest on Finance Leases     2.7    
Total Obligations Under Finance Leases     18.2 18.9  
Operating Lease Liabilities Rolling Future Minimum Lease Payments          
Year 1     16.9    
Year 2     15.3    
Year 3     14.1    
Year 4     12.8    
Year 5     10.6    
Operating Leases, Later Years     9.1    
Operating Leases, Total Future Minimum Lease Payments     78.8    
Imputed Interest on Operating Leases     8.6    
Estimated Present Value of Future Minimum Lease Payments on Operating Leases     70.2 73.8  
Maximum Potential Loss          
Max Potential Loss on Master Lease Agreements     7.2    
Leases (Textuals)          
Repayments of Long-term Debt     0.6 0.1 500.1
Ohio Power Co [Member] | Finance Lease Assets [Member]          
Property, Plant and Equipment and Other Related Obligations Under Finance Leases          
Generation     0.0 0.0  
Other Property, Plant and Equipment     33.7 32.7  
Total Property, Plant and Equipment     33.7 32.7  
Accumulated Amortization     15.5 13.8  
Ohio Power Co [Member] | Finance Lease Liabilities [Member]          
Property, Plant and Equipment and Other Related Obligations Under Finance Leases          
Other Liabilities, Noncurrent     13.2 14.2  
Finance Lease Liability Due Within One Year     5.0 4.7  
Ohio Power Co [Member] | Operating Lease Assets [Member]          
Operating Lease Asset and Related Obligations          
Operating Lease Assets     69.9 73.8  
Public Service Co Of Oklahoma [Member]          
Lease Rental Costs          
Operating Lease, Cost     13.5 11.8 8.7
Finance Lease Right-of-Use Asset Amortization     3.3 3.2 3.2
Interest Expense on Finance Leases     0.7 0.6 0.6
Total Lease Rental Costs [1]     $ 17.5 $ 15.6 12.5
Supplemental Information Related to Leases          
Weighted-Average Remaining Lease Term, Operating Leases     23 years 10 months 6 days 23 years 10 months 24 days  
Weighted Average Remaining Lease Term, Finance Leases     5 years 9 months 3 days 6 years 7 days  
Weighted Average Discount Rate, Operating Leases     3.72% 3.43%  
Weighted Average Discount Rate, Finance Leases     5.14% 4.63%  
Operating Cash Flows Used for Operating Leases     $ 12.5 $ 10.5  
Operating Cash Flows Used for Finance Leases     0.7 0.6  
Financing Cash Flows Used for Finance Leases     3.3 3.2 3.2
Non-cash Acquisitions Under Operating Leases     15.5 46.0  
Property, Plant and Equipment and Other Related Obligations Under Finance Leases          
Generation     2,695.5 2,394.8  
Other Property, Plant and Equipment     505.9 469.3  
Total Property, Plant and Equipment     8,194.2 7,464.2  
Accumulated Amortization     2,081.9 1,837.7  
Net Property, Plant and Equipment Under Finance Leases     13.8 15.0  
Other Liabilities, Noncurrent     33.8 21.3  
Finance Lease Liability Due Within One Year     106.2 82.0  
Total Obligations Under Finance Leases     13.8 15.0  
Operating Lease Asset and Related Obligations          
Operating Lease Assets     112.8 106.1  
Operating Lease Noncurrent Liability     106.8 99.3  
Operating Lease Liability Due Within One Year     10.1 8.9  
Estimated Present Value of Future Minimum Lease Payments on Operating Leases     116.9 108.2  
Finance Lease Liabilities Rolling Future Minimum Lease Payments          
Year 1     3.7    
Year 2     2.9    
Year 3     2.5    
Year 4     2.0    
Year 5     1.7    
Finance Leases, Later Years     3.3    
Finance Leases, Total Future Minimum Lease Payments     16.1    
Imputed Interest on Finance Leases     2.3    
Total Obligations Under Finance Leases     13.8 15.0  
Operating Lease Liabilities Rolling Future Minimum Lease Payments          
Year 1     12.2    
Year 2     11.1    
Year 3     10.3    
Year 4     9.3    
Year 5     7.9    
Operating Leases, Later Years     129.1    
Operating Leases, Total Future Minimum Lease Payments     179.9    
Imputed Interest on Operating Leases     63.0    
Estimated Present Value of Future Minimum Lease Payments on Operating Leases     116.9 108.2  
Maximum Potential Loss          
Max Potential Loss on Master Lease Agreements     4.7    
Leases (Textuals)          
Repayments of Long-term Debt     0.5 500.5 750.5
Public Service Co Of Oklahoma [Member] | Finance Lease Assets [Member]          
Property, Plant and Equipment and Other Related Obligations Under Finance Leases          
Generation     0.6 0.6  
Other Property, Plant and Equipment     25.5 25.2  
Total Property, Plant and Equipment     26.1 25.8  
Accumulated Amortization     12.3 10.8  
Public Service Co Of Oklahoma [Member] | Finance Lease Liabilities [Member]          
Property, Plant and Equipment and Other Related Obligations Under Finance Leases          
Other Liabilities, Noncurrent     10.7 11.7  
Finance Lease Liability Due Within One Year     3.1 3.3  
Public Service Co Of Oklahoma [Member] | Operating Lease Assets [Member]          
Operating Lease Asset and Related Obligations          
Operating Lease Assets     112.8 106.1  
Southwestern Electric Power Co [Member]          
Lease Rental Costs          
Operating Lease, Cost     17.5 15.3 12.1
Finance Lease Right-of-Use Asset Amortization     19.9 10.8 11.0
Interest Expense on Finance Leases     1.4 2.1 2.5
Total Lease Rental Costs [1]     $ 38.8 $ 28.2 25.6
Supplemental Information Related to Leases          
Weighted-Average Remaining Lease Term, Operating Leases     22 years 6 months 23 years 6 months 18 days  
Weighted Average Remaining Lease Term, Finance Leases     4 years 9 months 10 days 4 years 1 month 17 days  
Weighted Average Discount Rate, Operating Leases     3.53% 3.41%  
Weighted Average Discount Rate, Finance Leases     5.22% 4.80%  
Operating Cash Flows Used for Operating Leases     $ 16.5 $ 13.7  
Operating Cash Flows Used for Finance Leases     1.4 2.1  
Financing Cash Flows Used for Finance Leases     19.1 10.8 10.9
Non-cash Acquisitions Under Operating Leases     14.3 53.6  
Property, Plant and Equipment and Other Related Obligations Under Finance Leases          
Generation     4,790.7 5,476.2  
Other Property, Plant and Equipment     814.4 804.4  
Total Property, Plant and Equipment     11,645.6 11,789.5  
Accumulated Amortization     3,087.2 3,527.3  
Net Property, Plant and Equipment Under Finance Leases     29.0 29.6  
Other Liabilities, Noncurrent     93.8 68.4  
Finance Lease Liability Due Within One Year     154.6 172.0  
Total Obligations Under Finance Leases     30.1 42.2  
Operating Lease Asset and Related Obligations          
Operating Lease Noncurrent Liability     122.5 120.2  
Operating Lease Liability Due Within One Year     9.0 8.4  
Estimated Present Value of Future Minimum Lease Payments on Operating Leases     131.5 128.6  
Finance Lease Liabilities Rolling Future Minimum Lease Payments          
Year 1     12.6    
Year 2     4.6    
Year 3     3.9    
Year 4     3.5    
Year 5     3.0    
Finance Leases, Later Years     7.2    
Finance Leases, Total Future Minimum Lease Payments     34.8    
Imputed Interest on Finance Leases     4.7    
Total Obligations Under Finance Leases     30.1 42.2  
Operating Lease Liabilities Rolling Future Minimum Lease Payments          
Year 1     16.2    
Year 2     15.0    
Year 3     12.9    
Year 4     11.5    
Year 5     9.5    
Operating Leases, Later Years     135.6    
Operating Leases, Total Future Minimum Lease Payments     200.7    
Imputed Interest on Operating Leases     69.2    
Estimated Present Value of Future Minimum Lease Payments on Operating Leases     131.5 128.6  
Maximum Potential Loss          
Max Potential Loss on Master Lease Agreements     5.4    
Leases (Textuals)          
Repayments of Long-term Debt     94.1 6.2 $ 381.2
Southwestern Electric Power Co [Member] | Finance Lease Assets [Member]          
Property, Plant and Equipment and Other Related Obligations Under Finance Leases          
Generation     25.3 25.9  
Other Property, Plant and Equipment     32.0 58.3  
Total Property, Plant and Equipment     57.3 84.2  
Accumulated Amortization     28.3 54.6  
Southwestern Electric Power Co [Member] | Finance Lease Liabilities [Member]          
Property, Plant and Equipment and Other Related Obligations Under Finance Leases          
Other Liabilities, Noncurrent     18.8 31.3  
Finance Lease Liability Due Within One Year     11.3 10.9  
Southwestern Electric Power Co [Member] | Operating Lease Assets [Member]          
Operating Lease Asset and Related Obligations          
Operating Lease Assets     $ 126.3 $ 123.4  
[1] Excludes variable and short-term lease costs, which were immaterial.