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Regulatory Matters (Regulatory Assets) (Details) - USD ($) $ in Millions | Mar. 31, 2022 | Dec. 31, 2021
--- | --- | ---
Regulatory Assets [Line Items] |  |
Regulatory assets | $ 1,919 | $ 1,940
Tax-related [Member] |  |
Regulatory Assets [Line Items] |  |
Regulatory assets | 949 | 934
Pension and OPEB costs [Member] |  |
Regulatory Assets [Line Items] |  |
Regulatory assets | 453 | 462
Asset retirement obligations [Member] |  |
Regulatory Assets [Line Items] |  |
Regulatory assets | 134 | 128
Assets retired early [Member] |  |
Regulatory Assets [Line Items] |  |
Regulatory assets | 88 | 92
IPL's DAEC PPA amendment [Member] |  |
Regulatory Assets [Line Items] |  |
Regulatory assets | 84 | 90
WPL's Western Wisconsin gas distribution expansion investments [Member] |  |
Regulatory Assets [Line Items] |  |
Regulatory assets | 50 | 52
Commodity cost recovery [Member] |  |
Regulatory Assets [Line Items] |  |
Regulatory assets | 42 | 42
Other [Member] |  |
Regulatory Assets [Line Items] |  |
Regulatory assets | 119 | 140
IPL [Member] |  |
Regulatory Assets [Line Items] |  |
Regulatory assets | 1,432 | 1,443
IPL [Member] | Tax-related [Member] |  |
Regulatory Assets [Line Items] |  |
Regulatory assets | 896 | 884
IPL [Member] | Pension and OPEB costs [Member] |  |
Regulatory Assets [Line Items] |  |
Regulatory assets | 224 | 228
IPL [Member] | Asset retirement obligations [Member] |  |
Regulatory Assets [Line Items] |  |
Regulatory assets | 94 | 89
IPL [Member] | Assets retired early [Member] |  |
Regulatory Assets [Line Items] |  |
Regulatory assets | 64 | 66
IPL [Member] | IPL's DAEC PPA amendment [Member] |  |
Regulatory Assets [Line Items] |  |
Regulatory assets | 84 | 90
IPL [Member] | Commodity cost recovery [Member] |  |
Regulatory Assets [Line Items] |  |
Regulatory assets | 2 | 2
IPL [Member] | Other [Member] |  |
Regulatory Assets [Line Items] |  |
Regulatory assets | 68 | 84
WPL [Member] |  |
Regulatory Assets [Line Items] |  |
Regulatory assets | 487 | 497
WPL [Member] | Tax-related [Member] |  |
Regulatory Assets [Line Items] |  |
Regulatory assets | 53 | 50
WPL [Member] | Pension and OPEB costs [Member] |  |
Regulatory Assets [Line Items] |  |
Regulatory assets | 229 | 234
WPL [Member] | Asset retirement obligations [Member] |  |
Regulatory Assets [Line Items] |  |
Regulatory assets | 40 | 39
WPL [Member] | Assets retired early [Member] |  |
Regulatory Assets [Line Items] |  |
Regulatory assets | 24 | 26
WPL [Member] | WPL's Western Wisconsin gas distribution expansion investments [Member] |  |
Regulatory Assets [Line Items] |  |
Regulatory assets | 50 | 52
WPL [Member] | Commodity cost recovery [Member] |  |
Regulatory Assets [Line Items] |  |
Regulatory assets | 40 | 40
WPL [Member] | Other [Member] |  |
Regulatory Assets [Line Items] |  |
Regulatory assets | $ 51 | $ 56

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