Supplemental Information (Inventories) (Details) - USD ($) $ in Millions	Dec. 31, 2024	Dec. 31, 2023
Public Utilities, Inventory [Line Items]
Fuel	$ 113	$ 109
Natural gas stored underground	91	95
Materials, supplies, and other	558	529
Total inventories	762	733
Ameren Missouri
Public Utilities, Inventory [Line Items]
Fuel	113	109
Natural gas stored underground	9	8
Materials, supplies, and other	392	391
Total inventories	514	508
Ameren Illinois
Public Utilities, Inventory [Line Items]
Fuel	0	0
Natural gas stored underground	82	87
Materials, supplies, and other	162	138
Total inventories	$ 244	$ 225