Nature of Operations And Summary of Significant Accounting Policies (Narrative) (Details) $ in Millions |
12 Months Ended | |||
|---|---|---|---|---|
|
Dec. 31, 2024
USD ($)
|
Dec. 31, 2023
USD ($)
|
Dec. 31, 2022 |
Jun. 17, 2023
Rate
|
|
| Basis Of Accounting Presentation [Line Items] | ||||
| Number of customers | 3,800,000 | |||
| Pre-tax rate for allowance for funds used during construction | 4.80% | 3.90% | 3.40% | |
| Inventory valued using LIFO | $ 43.8 | $ 43.9 | ||
| Excess of replacement over LIFO value | (12.8) | (22.5) | ||
| Inventory valued using the weighted average cost methodology | $ 135.8 | $ 222.0 | ||
| NIPSCO Holdings II | ||||
| Basis Of Accounting Presentation [Line Items] | ||||
| Subsidiary, Ownership Percentage, Parent | Rate | 19.90% | |||