Derivative Financial Instruments (Offsetting Assets and Liabilities) (Details) - Not Designated As Hedging Instrument - USD ($) $ in Millions	Jun. 30, 2023	Dec. 31, 2022
Derivative [Line Items]
Gross derivative asset amount recognized on the balance sheet	$ 43	$ 89
Gross derivative instruments not offset in the balance sheet	18	29
Gross cash collateral received not offset in the balance sheet	0	0
Net derivative asset	25	60
Gross derivative liability amount recognized on the balance sheet	145	136
Gross derivative instruments not offset in the balance sheet	18	29
Gross cash collateral posted not offset in the balance sheet	12	56
Net derivative liability	115	51
Union Electric Company
Derivative [Line Items]
Gross derivative asset amount recognized on the balance sheet	30	49
Gross derivative instruments not offset in the balance sheet	9	9
Gross cash collateral received not offset in the balance sheet	0	0
Net derivative asset	21	40
Gross derivative liability amount recognized on the balance sheet	31	68
Gross derivative instruments not offset in the balance sheet	9	9
Gross cash collateral posted not offset in the balance sheet	12	56
Net derivative liability	10	3
Ameren Illinois Company
Derivative [Line Items]
Gross derivative asset amount recognized on the balance sheet	13	40
Gross derivative instruments not offset in the balance sheet	9	20
Gross cash collateral received not offset in the balance sheet	0	0
Net derivative asset	4	20
Gross derivative liability amount recognized on the balance sheet	114	68
Gross derivative instruments not offset in the balance sheet	9	20
Gross cash collateral posted not offset in the balance sheet	0	0
Net derivative liability	$ 105	$ 48