Related Party Transactions (Schedule of Affiliate Receivables and Payables) (Details) - USD ($) $ in Millions	Mar. 31, 2023	Dec. 31, 2022
Union Electric Company
Related Party Transaction [Line Items]
Accounts Payable, Related Parties, Current	$ 36	$ 43
Accounts Receivable, Related Parties, Current	70	51
Union Electric Company | Income taxes payable to parent
Related Party Transaction [Line Items]
Accounts Payable, Related Parties, Current	0	0
Union Electric Company | Income taxes receivable from parent
Related Party Transaction [Line Items]
Accounts Receivable, Related Parties, Current	54	39
Ameren Illinois Company
Related Party Transaction [Line Items]
Accounts Payable, Related Parties, Current	117	93
Accounts Receivable, Related Parties, Current	14	12
Ameren Illinois Company | Income taxes payable to parent
Related Party Transaction [Line Items]
Accounts Payable, Related Parties, Current	80	50
Ameren Illinois Company | Income taxes receivable from parent
Related Party Transaction [Line Items]
Accounts Receivable, Related Parties, Current	$ 0	$ 0