Derivative Instruments (Balance Sheet Offsetting) (Details) - Commodity Contracts [Member] - USD ($) $ in Millions	Sep. 30, 2025	Dec. 31, 2024
Derivative Instruments [Line Items]
Derivative assets, Gross (as reported)	$ 82	$ 75
Derivative assets, Net	72	64
Derivative liabilities, Gross (as reported)	48	58
Derivative liabilities, Net	38	47
IPL [Member]
Derivative Instruments [Line Items]
Derivative assets, Gross (as reported)	52	48
Derivative assets, Net	47	43
Derivative liabilities, Gross (as reported)	10	13
Derivative liabilities, Net	5	8
WPL [Member]
Derivative Instruments [Line Items]
Derivative assets, Gross (as reported)	30	27
Derivative assets, Net	25	21
Derivative liabilities, Gross (as reported)	38	45
Derivative liabilities, Net	$ 33	$ 39

Fair value, before effects of master netting arrangements, of a financial asset or other contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset. Includes assets elected not to be offset. Excludes assets not subject to a master netting arrangement.

Fair value, before effects of master netting arrangements, of a financial liability or contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset. Includes liabilities elected not to be offset. Excludes liabilities not subject to a master netting arrangement.

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