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Regulatory Matters (Regulatory Assets) (Details) - USD ($) $ in Millions | Sep. 30, 2023 | Dec. 31, 2022
--- | --- | ---
Regulatory Assets [Line Items] |  |
Regulatory assets | $ 2,269 | $ 2,046
Tax-related [Member] |  |
Regulatory Assets [Line Items] |  |
Regulatory assets | 919 | 929
Pension and OPEB costs [Member] |  |
Regulatory Assets [Line Items] |  |
Regulatory assets | 371 | 392
Assets retired early [Member] |  |
Regulatory Assets [Line Items] |  |
Regulatory assets | 282 | 70
Asset retirement obligations [Member] |  |
Regulatory Assets [Line Items] |  |
Regulatory assets | 199 | 151
Commodity cost recovery [Member] |  |
Regulatory Assets [Line Items] |  |
Regulatory assets | 138 | 160
Derivatives [Member] |  |
Regulatory Assets [Line Items] |  |
Regulatory assets | 72 | 84
IPL's Duane Arnold Energy Center PPA amendment [Member] |  |
Regulatory Assets [Line Items] |  |
Regulatory assets | 48 | 66
WPL's Western Wisconsin gas distribution expansion investments [Member] |  |
Regulatory Assets [Line Items] |  |
Regulatory assets | 46 | 48
Other [Member] |  |
Regulatory Assets [Line Items] |  |
Regulatory assets | 194 | 146
IPL [Member] |  |
Regulatory Assets [Line Items] |  |
Regulatory assets | 1,590 | 1,386
IPL [Member] | Tax-related [Member] |  |
Regulatory Assets [Line Items] |  |
Regulatory assets | 825 | 848
IPL [Member] | Pension and OPEB costs [Member] |  |
Regulatory Assets [Line Items] |  |
Regulatory assets | 187 | 197
IPL [Member] | Assets retired early [Member] |  |
Regulatory Assets [Line Items] |  |
Regulatory assets | 267 | 53
IPL [Member] | Asset retirement obligations [Member] |  |
Regulatory Assets [Line Items] |  |
Regulatory assets | 155 | 110
IPL [Member] | Commodity cost recovery [Member] |  |
Regulatory Assets [Line Items] |  |
Regulatory assets | 11 | 1
IPL [Member] | Derivatives [Member] |  |
Regulatory Assets [Line Items] |  |
Regulatory assets | 27 | 48
IPL [Member] | IPL's Duane Arnold Energy Center PPA amendment [Member] |  |
Regulatory Assets [Line Items] |  |
Regulatory assets | 48 | 66
IPL [Member] | Other [Member] |  |
Regulatory Assets [Line Items] |  |
Regulatory assets | 70 | 63
WPL [Member] |  |
Regulatory Assets [Line Items] |  |
Regulatory assets | 679 | 660
WPL [Member] | Tax-related [Member] |  |
Regulatory Assets [Line Items] |  |
Regulatory assets | 94 | 81
WPL [Member] | Pension and OPEB costs [Member] |  |
Regulatory Assets [Line Items] |  |
Regulatory assets | 184 | 195
WPL [Member] | Assets retired early [Member] |  |
Regulatory Assets [Line Items] |  |
Regulatory assets | 15 | 17
WPL [Member] | Asset retirement obligations [Member] |  |
Regulatory Assets [Line Items] |  |
Regulatory assets | 44 | 41
WPL [Member] | Commodity cost recovery [Member] |  |
Regulatory Assets [Line Items] |  |
Regulatory assets | 127 | 159
WPL [Member] | Derivatives [Member] |  |
Regulatory Assets [Line Items] |  |
Regulatory assets | 45 | 36
WPL [Member] | WPL's Western Wisconsin gas distribution expansion investments [Member] |  |
Regulatory Assets [Line Items] |  |
Regulatory assets | 46 | 48
WPL [Member] | Other [Member] |  |
Regulatory Assets [Line Items] |  |
Regulatory assets | $ 124 | $ 83

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