Related Party Transactions (Narrative) (Details) - Ameren Services Support Services Agreement - USD ($) $ in Millions	Mar. 31, 2022	Dec. 31, 2021
Union Electric Company
Related Party Transaction [Line Items]
Due from Related Parties	$ 77	$ 77
Ameren Illinois Company
Related Party Transaction [Line Items]
Due from Related Parties	$ 80	$ 80

For an unclassified balance sheet, amounts due from related parties including affiliates, employees, joint ventures, officers and stockholders, immediate families thereof, and pension funds.

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+ Details