Supplemental Information (Inventories) (Details) - USD ($) $ in Millions	Dec. 31, 2022	Dec. 31, 2021
Public Utilities, Inventory [Line Items]
Fuel	$ 79	$ 118
Natural gas stored underground	130	99
Materials, supplies, and other	458	375
Total inventories	667	592
Union Electric Company
Public Utilities, Inventory [Line Items]
Fuel	79	118
Natural gas stored underground	10	9
Materials, supplies, and other	345	292
Total inventories	434	419
Ameren Illinois Company
Public Utilities, Inventory [Line Items]
Fuel	0	0
Natural gas stored underground	120	90
Materials, supplies, and other	113	83
Total inventories	$ 233	$ 173