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Regulatory Matters (Regulatory Assets) (Details) - USD ($) $ in Millions | Sep. 30, 2025 | Dec. 31, 2024
--- | --- | ---
Regulatory Assets [Line Items] |  |
Regulatory assets | $ 2,303 | $ 2,274
Tax-related [Member] |  |
Regulatory Assets [Line Items] |  |
Regulatory assets | 1,069 | 989
AROs [Member] |  |
Regulatory Assets [Line Items] |  |
Regulatory assets | 441 | 401
Pension and OPEB costs [Member] |  |
Regulatory Assets [Line Items] |  |
Regulatory assets | 301 | 315
Assets retired early [Member] |  |
Regulatory Assets [Line Items] |  |
Regulatory assets | 162 | 180
Non-service pension and OPEB costs [Member] |  |
Regulatory Assets [Line Items] |  |
Regulatory assets | 55 | 51
Derivatives [Member] |  |
Regulatory Assets [Line Items] |  |
Regulatory assets | 51 | 60
WPL's Western Wisconsin gas distribution expansion investments [Member] |  |
Regulatory Assets [Line Items] |  |
Regulatory assets | 40 | 42
Commodity cost recovery [Member] |  |
Regulatory Assets [Line Items] |  |
Regulatory assets | 33 | 68
Other [Member] |  |
Regulatory Assets [Line Items] |  |
Regulatory assets | 151 | 168
IPL [Member] |  |
Regulatory Assets [Line Items] |  |
Regulatory assets | 1,632 | 1,586
IPL [Member] | Tax-related [Member] |  |
Regulatory Assets [Line Items] |  |
Regulatory assets | 932 | 870
IPL [Member] | AROs [Member] |  |
Regulatory Assets [Line Items] |  |
Regulatory assets | 304 | 281
IPL [Member] | Pension and OPEB costs [Member] |  |
Regulatory Assets [Line Items] |  |
Regulatory assets | 151 | 157
IPL [Member] | Assets retired early [Member] |  |
Regulatory Assets [Line Items] |  |
Regulatory assets | 153 | 168
IPL [Member] | Non-service pension and OPEB costs [Member] |  |
Regulatory Assets [Line Items] |  |
Regulatory assets | 20 | 19
IPL [Member] | Derivatives [Member] |  |
Regulatory Assets [Line Items] |  |
Regulatory assets | 12 | 15
IPL [Member] | Commodity cost recovery [Member] |  |
Regulatory Assets [Line Items] |  |
Regulatory assets | 8 | 2
IPL [Member] | Other [Member] |  |
Regulatory Assets [Line Items] |  |
Regulatory assets | 52 | 74
WPL [Member] |  |
Regulatory Assets [Line Items] |  |
Regulatory assets | 671 | 688
WPL [Member] | Tax-related [Member] |  |
Regulatory Assets [Line Items] |  |
Regulatory assets | 137 | 119
WPL [Member] | AROs [Member] |  |
Regulatory Assets [Line Items] |  |
Regulatory assets | 137 | 120
WPL [Member] | Pension and OPEB costs [Member] |  |
Regulatory Assets [Line Items] |  |
Regulatory assets | 150 | 158
WPL [Member] | Assets retired early [Member] |  |
Regulatory Assets [Line Items] |  |
Regulatory assets | 9 | 12
WPL [Member] | Non-service pension and OPEB costs [Member] |  |
Regulatory Assets [Line Items] |  |
Regulatory assets | 35 | 32
WPL [Member] | Derivatives [Member] |  |
Regulatory Assets [Line Items] |  |
Regulatory assets | 39 | 45
WPL [Member] | WPL's Western Wisconsin gas distribution expansion investments [Member] |  |
Regulatory Assets [Line Items] |  |
Regulatory assets | 40 | 42
WPL [Member] | Commodity cost recovery [Member] |  |
Regulatory Assets [Line Items] |  |
Regulatory assets | 25 | 66
WPL [Member] | Other [Member] |  |
Regulatory Assets [Line Items] |  |
Regulatory assets | $ 99 | $ 94

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