Supplemental Information (Cash and Cash Equivalents) (Details) - USD ($) $ in Millions	Mar. 31, 2025	Dec. 31, 2024	Mar. 31, 2024	Dec. 31, 2023
Schedule of Cash and Cash Equivalents Including Restricted Cash [Line Items]
Cash and cash equivalents	$ 23	$ 7
Restricted cash included in “Other current assets”	40	15
Restricted cash included in “Other assets”	307	296
Restricted cash included in “Nuclear decommissioning trust fund”	6	10
Total cash, cash equivalents, and restricted cash	376	328	$ 355	$ 272
Union Electric Company
Schedule of Cash and Cash Equivalents Including Restricted Cash [Line Items]
Cash and cash equivalents	7	0
Restricted cash included in “Other current assets”	32	7
Restricted cash included in “Other assets”	0	0
Restricted cash included in “Nuclear decommissioning trust fund”	6	10
Total cash, cash equivalents, and restricted cash	45	17	16	10
Ameren Illinois Company
Schedule of Cash and Cash Equivalents Including Restricted Cash [Line Items]
Cash and cash equivalents	4	0
Restricted cash included in “Other current assets”	5	6
Restricted cash included in “Other assets”	307	296
Restricted cash included in “Nuclear decommissioning trust fund”	0	0
Total cash, cash equivalents, and restricted cash	$ 316	$ 302	$ 254	$ 234