Supplemental Information (Cash and Cash Equivalents) (Details) - USD ($) $ in Millions	Mar. 31, 2024	Dec. 31, 2023	Mar. 31, 2023	Dec. 31, 2022
Schedule of Cash and Cash Equivalents Including Restricted Cash [Line Items]
Cash and cash equivalents	$ 85	$ 25
Restricted cash included in “Other current assets”	13	13
Restricted cash included in “Other assets”	248	229
Restricted cash included in “Nuclear decommissioning trust fund”	9	5
Total cash, cash equivalents, and restricted cash	355	272	$ 237	$ 216
Union Electric Company
Schedule of Cash and Cash Equivalents Including Restricted Cash [Line Items]
Cash and cash equivalents	2	0
Restricted cash included in “Other current assets”	5	5
Restricted cash included in “Other assets”	0	0
Restricted cash included in “Nuclear decommissioning trust fund”	9	5
Total cash, cash equivalents, and restricted cash	16	10	11	13
Ameren Illinois Company
Schedule of Cash and Cash Equivalents Including Restricted Cash [Line Items]
Cash and cash equivalents	0	0
Restricted cash included in “Other current assets”	6	5
Restricted cash included in “Other assets”	248	229
Restricted cash included in “Nuclear decommissioning trust fund”	0	0
Total cash, cash equivalents, and restricted cash	$ 254	$ 234	$ 217	$ 191