Related Party Transactions (Narrative) (Details) - USD ($) $ in Millions	Jun. 30, 2025	Dec. 31, 2024
Related Party Transaction [Line Items]
Other assets	$ 1,110	$ 1,123
Union Electric Company
Related Party Transaction [Line Items]
Other assets	238	254
Ameren Illinois Company
Related Party Transaction [Line Items]
Other assets	739	697
Ameren Services Support Services Agreement \| Union Electric Company \| Related Party
Related Party Transaction [Line Items]
Other assets	20	29
Ameren Services Support Services Agreement \| Ameren Illinois Company \| Related Party
Related Party Transaction [Line Items]
Other assets	$ 22	$ 32

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.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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Reference 2: http://www.xbrl.org/2003/role/disclosureRef
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Reference 3: http://www.xbrl.org/2003/role/disclosureRef
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+ Details