Derivative Financial Instruments (Offsetting Assets and Liabilities) (Details) - Not Designated As Hedging Instrument - USD ($) $ in Millions	Dec. 31, 2023	Dec. 31, 2022
Derivative [Line Items]
Derivative Asset, Fair Value, Gross Asset	$ 22	$ 89
Derivative Liability, Fair Value, Gross Liability	168	136
Derivative, Collateral, Obligation to Return Securities	7	29
Derivative, Collateral, Right to Reclaim Securities	7	29
Derivative Asset, Collateral, Obligation to Return Cash, Offset	0	0
Derivative Liability, Collateral, Right to Reclaim Cash, Offset	6	56
Derivative Asset	15	60
Derivative Liability	155	51
Ameren Missouri
Derivative [Line Items]
Derivative Asset, Fair Value, Gross Asset	19	49
Derivative Liability, Fair Value, Gross Liability	25	68
Derivative, Collateral, Obligation to Return Securities	6	9
Derivative, Collateral, Right to Reclaim Securities	6	9
Derivative Asset, Collateral, Obligation to Return Cash, Offset	0	0
Derivative Liability, Collateral, Right to Reclaim Cash, Offset	0	56
Derivative Asset	13	40
Derivative Liability	19	3
Ameren Illinois
Derivative [Line Items]
Derivative Asset, Fair Value, Gross Asset	3	40
Derivative Liability, Fair Value, Gross Liability	143	68
Derivative, Collateral, Obligation to Return Securities	1	20
Derivative, Collateral, Right to Reclaim Securities	1	20
Derivative Asset, Collateral, Obligation to Return Cash, Offset	0	0
Derivative Liability, Collateral, Right to Reclaim Cash, Offset	6	0
Derivative Asset	2	20
Derivative Liability	$ 136	$ 48