Derivative Financial Instruments (Offsetting Assets and Liabilities) (Details) - Not Designated As Hedging Instrument - USD ($) $ in Millions	Jun. 30, 2024	Dec. 31, 2023
Derivative [Line Items]
Gross derivative asset amount recognized on the balance sheet	$ 24	$ 22
Gross derivative instruments not offset in the balance sheet	7	7
Gross cash collateral received not offset in the balance sheet	0	0
Net derivative asset	17	15
Gross derivative liability amount recognized on the balance sheet	141	168
Gross derivative instruments not offset in the balance sheet	7	7
Gross cash collateral posted not offset in the balance sheet	0	6
Net derivative liability	134	155
Union Electric Company
Derivative [Line Items]
Gross derivative asset amount recognized on the balance sheet	20	19
Gross derivative instruments not offset in the balance sheet	5	6
Gross cash collateral received not offset in the balance sheet	0	0
Net derivative asset	15	13
Gross derivative liability amount recognized on the balance sheet	19	25
Gross derivative instruments not offset in the balance sheet	5	6
Gross cash collateral posted not offset in the balance sheet	0	0
Net derivative liability	14	19
Ameren Illinois Company
Derivative [Line Items]
Gross derivative asset amount recognized on the balance sheet	4	3
Gross derivative instruments not offset in the balance sheet	2	1
Gross cash collateral received not offset in the balance sheet	0	0
Net derivative asset	2	2
Gross derivative liability amount recognized on the balance sheet	122	143
Gross derivative instruments not offset in the balance sheet	2	1
Gross cash collateral posted not offset in the balance sheet	0	6
Net derivative liability	$ 120	$ 136