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Regulatory Matters (Regulatory Assets) (Details) - USD ($) $ in Millions | Mar. 31, 2024 | Dec. 31, 2023
--- | --- | ---
Regulatory Assets [Line Items] |  |
Regulatory assets | $ 2,220 | $ 2,261
Tax-related [Member] |  |
Regulatory Assets [Line Items] |  |
Regulatory assets | 939 | 934
Pension and OPEB costs [Member] |  |
Regulatory Assets [Line Items] |  |
Regulatory assets | 340 | 347
Assets retired early [Member] |  |
Regulatory Assets [Line Items] |  |
Regulatory assets | 267 | 273
Asset retirement obligations [Member] |  |
Regulatory Assets [Line Items] |  |
Regulatory assets | 200 | 194
Commodity cost recovery [Member] |  |
Regulatory Assets [Line Items] |  |
Regulatory assets | 100 | 120
Derivatives [Member] |  |
Regulatory Assets [Line Items] |  |
Regulatory assets | 97 | 102
WPL's Western Wisconsin gas distribution expansion investments [Member] |  |
Regulatory Assets [Line Items] |  |
Regulatory assets | 44 | 44
IPL's Duane Arnold Energy Center PPA amendment [Member] |  |
Regulatory Assets [Line Items] |  |
Regulatory assets | 36 | 42
Other [Member] |  |
Regulatory Assets [Line Items] |  |
Regulatory assets | 197 | 205
IPL [Member] |  |
Regulatory Assets [Line Items] |  |
Regulatory assets | 1,567 | 1,577
IPL [Member] | Tax-related [Member] |  |
Regulatory Assets [Line Items] |  |
Regulatory assets | 839 | 831
IPL [Member] | Pension and OPEB costs [Member] |  |
Regulatory Assets [Line Items] |  |
Regulatory assets | 168 | 171
IPL [Member] | Assets retired early [Member] |  |
Regulatory Assets [Line Items] |  |
Regulatory assets | 253 | 259
IPL [Member] | Asset retirement obligations [Member] |  |
Regulatory Assets [Line Items] |  |
Regulatory assets | 165 | 160
IPL [Member] | Commodity cost recovery [Member] |  |
Regulatory Assets [Line Items] |  |
Regulatory assets | 5 | 12
IPL [Member] | Derivatives [Member] |  |
Regulatory Assets [Line Items] |  |
Regulatory assets | 33 | 34
IPL [Member] | IPL's Duane Arnold Energy Center PPA amendment [Member] |  |
Regulatory Assets [Line Items] |  |
Regulatory assets | 36 | 42
IPL [Member] | Other [Member] |  |
Regulatory Assets [Line Items] |  |
Regulatory assets | 68 | 68
WPL [Member] |  |
Regulatory Assets [Line Items] |  |
Regulatory assets | 653 | 684
WPL [Member] | Tax-related [Member] |  |
Regulatory Assets [Line Items] |  |
Regulatory assets | 100 | 103
WPL [Member] | Pension and OPEB costs [Member] |  |
Regulatory Assets [Line Items] |  |
Regulatory assets | 172 | 176
WPL [Member] | Assets retired early [Member] |  |
Regulatory Assets [Line Items] |  |
Regulatory assets | 14 | 14
WPL [Member] | Asset retirement obligations [Member] |  |
Regulatory Assets [Line Items] |  |
Regulatory assets | 35 | 34
WPL [Member] | Commodity cost recovery [Member] |  |
Regulatory Assets [Line Items] |  |
Regulatory assets | 95 | 108
WPL [Member] | Derivatives [Member] |  |
Regulatory Assets [Line Items] |  |
Regulatory assets | 64 | 68
WPL [Member] | WPL's Western Wisconsin gas distribution expansion investments [Member] |  |
Regulatory Assets [Line Items] |  |
Regulatory assets | 44 | 44
WPL [Member] | Other [Member] |  |
Regulatory Assets [Line Items] |  |
Regulatory assets | $ 129 | $ 137

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