Derivative Financial Instruments (Offsetting Assets and Liabilities) (Details) - Not Designated As Hedging Instrument - USD ($) $ in Millions	Mar. 31, 2025	Dec. 31, 2024
Derivative [Line Items]
Gross derivative asset amount recognized on the balance sheet	$ 27	$ 16
Gross derivative liability amount recognized on the balance sheet	99	103
Union Electric Company
Derivative [Line Items]
Gross derivative asset amount recognized on the balance sheet	11	10
Gross derivative liability amount recognized on the balance sheet	12	15
Ameren Illinois Company
Derivative [Line Items]
Gross derivative asset amount recognized on the balance sheet	16	6
Gross derivative liability amount recognized on the balance sheet	$ 87	$ 88

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.

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Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant