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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

X

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

+ Details

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- Definition

The amount for the individual regulatory asset as itemized in a table of regulatory assets as of the end of the period.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Topic 980
-SubTopic 340
-Name Accounting Standards Codification
-Section 50
-Paragraph 1
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147478742/980-340-50-1

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