Regulatory Matters (Regulatory Assets) (Details) - USD ($) $ in Millions	Mar. 31, 2025	Dec. 31, 2024
Regulatory Assets [Line Items]
Regulatory assets	$ 2,274	$ 2,274
Tax-related [Member]
Regulatory Assets [Line Items]
Regulatory assets	1,011	989
Asset retirement obligations (AROs) [Member]
Regulatory Assets [Line Items]
Regulatory assets	414	401
Pension and OPEB costs [Member]
Regulatory Assets [Line Items]
Regulatory assets	312	315
Assets retired early [Member]
Regulatory Assets [Line Items]
Regulatory assets	173	180
Commodity cost recovery [Member]
Regulatory Assets [Line Items]
Regulatory assets	56	68
Derivatives [Member]
Regulatory Assets [Line Items]
Regulatory assets	53	60
Non-service pension and OPEB costs [Member]
Regulatory Assets [Line Items]
Regulatory assets	53	51
WPL's Western Wisconsin gas distribution expansion investments [Member]
Regulatory Assets [Line Items]
Regulatory assets	41	42
Other [Member]
Regulatory Assets [Line Items]
Regulatory assets	161	168
IPL [Member]
Regulatory Assets [Line Items]
Regulatory assets	1,593	1,586
IPL [Member] | Tax-related [Member]
Regulatory Assets [Line Items]
Regulatory assets	884	870
IPL [Member] | Asset retirement obligations (AROs) [Member]
Regulatory Assets [Line Items]
Regulatory assets	289	281
IPL [Member] | Pension and OPEB costs [Member]
Regulatory Assets [Line Items]
Regulatory assets	156	157
IPL [Member] | Assets retired early [Member]
Regulatory Assets [Line Items]
Regulatory assets	162	168
IPL [Member] | Commodity cost recovery [Member]
Regulatory Assets [Line Items]
Regulatory assets	2	2
IPL [Member] | Derivatives [Member]
Regulatory Assets [Line Items]
Regulatory assets	11	15
IPL [Member] | Non-service pension and OPEB costs [Member]
Regulatory Assets [Line Items]
Regulatory assets	20	19
IPL [Member] | Other [Member]
Regulatory Assets [Line Items]
Regulatory assets	69	74
WPL [Member]
Regulatory Assets [Line Items]
Regulatory assets	681	688
WPL [Member] | Tax-related [Member]
Regulatory Assets [Line Items]
Regulatory assets	127	119
WPL [Member] | Asset retirement obligations (AROs) [Member]
Regulatory Assets [Line Items]
Regulatory assets	125	120
WPL [Member] | Pension and OPEB costs [Member]
Regulatory Assets [Line Items]
Regulatory assets	156	158
WPL [Member] | Assets retired early [Member]
Regulatory Assets [Line Items]
Regulatory assets	11	12
WPL [Member] | Commodity cost recovery [Member]
Regulatory Assets [Line Items]
Regulatory assets	54	66
WPL [Member] | Derivatives [Member]
Regulatory Assets [Line Items]
Regulatory assets	42	45
WPL [Member] | Non-service pension and OPEB costs [Member]
Regulatory Assets [Line Items]
Regulatory assets	33	32
WPL [Member] | WPL's Western Wisconsin gas distribution expansion investments [Member]
Regulatory Assets [Line Items]
Regulatory assets	41	42
WPL [Member] | Other [Member]
Regulatory Assets [Line Items]
Regulatory assets	$ 92	$ 94