Supplemental Information (Cash and Cash Equivalents) (Details) - USD ($) $ in Millions	Jun. 30, 2024	Dec. 31, 2023	Jun. 30, 2023	Dec. 31, 2022
Schedule of Cash and Cash Equivalents Including Restricted Cash [Line Items]
Cash and cash equivalents	$ 19	$ 25
Restricted cash included in “Other current assets”	18	13
Restricted cash included in “Other assets”	260	229
Restricted cash included in “Nuclear decommissioning trust fund”	4	5
Total cash, cash equivalents, and restricted cash	301	272	$ 246	$ 216
Union Electric 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”	7	5
Restricted cash included in “Other assets”	0	0
Restricted cash included in “Nuclear decommissioning trust fund”	4	5
Total cash, cash equivalents, and restricted cash	11	10	8	13
Ameren Illinois Company
Schedule of Cash and Cash Equivalents Including Restricted Cash [Line Items]
Cash and cash equivalents	6	0
Restricted cash included in “Other current assets”	7	5
Restricted cash included in “Other assets”	260	229
Restricted cash included in “Nuclear decommissioning trust fund”	0	0
Total cash, cash equivalents, and restricted cash	$ 273	$ 234	$ 229	$ 191