Derivative Financial Instruments (Offsetting Assets and Liabilities) (Details) - Not Designated As Hedging Instrument - USD ($) $ in Millions	Dec. 31, 2022	Dec. 31, 2021
Derivative [Line Items]
Derivative Asset, Fair Value, Gross Asset	$ 89	$ 90
Derivative Liability, Fair Value, Gross Liability	136	202
Derivative, Collateral, Obligation to Return Securities	29	19
Derivative, Collateral, Right to Reclaim Securities	29	19
Derivative Asset, Collateral, Obligation to Return Cash, Offset	0	0
Derivative Liability, Collateral, Right to Reclaim Cash, Offset	56	47
Derivative Asset	60	71
Derivative Liability	51	136
Union Electric Company
Derivative [Line Items]
Derivative Asset, Fair Value, Gross Asset	49	49
Derivative Liability, Fair Value, Gross Liability	68	77
Derivative, Collateral, Obligation to Return Securities	9	15
Derivative, Collateral, Right to Reclaim Securities	9	15
Derivative Asset, Collateral, Obligation to Return Cash, Offset	0	0
Derivative Liability, Collateral, Right to Reclaim Cash, Offset	56	47
Derivative Asset	40	34
Derivative Liability	3	15
Ameren Illinois Company
Derivative [Line Items]
Derivative Asset, Fair Value, Gross Asset	40	41
Derivative Liability, Fair Value, Gross Liability	68	125
Derivative, Collateral, Obligation to Return Securities	20	4
Derivative, Collateral, Right to Reclaim Securities	20	4
Derivative Asset, Collateral, Obligation to Return Cash, Offset	0	0
Derivative Liability, Collateral, Right to Reclaim Cash, Offset	0	0
Derivative Asset	20	37
Derivative Liability	$ 48	$ 121