Supplemental Information (Inventories) (Details) - USD ($) $ in Millions	Dec. 31, 2023	Dec. 31, 2022
Public Utilities, Inventory [Line Items]
Fuel	$ 109	$ 79
Natural gas stored underground	95	130
Materials, supplies, and other	529	458
Total inventories	733	667
Ameren Missouri
Public Utilities, Inventory [Line Items]
Fuel	109	79
Natural gas stored underground	8	10
Materials, supplies, and other	391	345
Total inventories	508	434
Ameren Illinois
Public Utilities, Inventory [Line Items]
Fuel	0	0
Natural gas stored underground	87	120
Materials, supplies, and other	138	113
Total inventories	$ 225	$ 233