Derivative Financial Instruments (Derivative Instruments Carrying Value) (Details) - Not Designated As Hedging Instrument - USD ($) $ in Millions	Dec. 31, 2022	Dec. 31, 2021
Derivative [Line Items]
Derivative assets	$ 89	$ 90
Derivative liabilities	136	202
Fuel oils | Other current assets
Derivative [Line Items]
Derivative assets	13	8
Fuel oils | Other assets
Derivative [Line Items]
Derivative assets	3	5
Natural gas | Other current assets
Derivative [Line Items]
Derivative assets	30	35
Natural gas | Other assets
Derivative [Line Items]
Derivative assets	20	18
Natural gas | Other current liabilities
Derivative [Line Items]
Derivative liabilities	27	8
Natural gas | Other deferred credits and liabilities
Derivative [Line Items]
Derivative liabilities	11	3
Power | Other current assets
Derivative [Line Items]
Derivative assets	16	23
Power | Other assets
Derivative [Line Items]
Derivative assets	4	0
Power | Other current liabilities
Derivative [Line Items]
Derivative liabilities	61	59
Power | Other deferred credits and liabilities
Derivative [Line Items]
Derivative liabilities	37	131
Uranium | Other current assets
Derivative [Line Items]
Derivative assets	2	0
Uranium | Other assets
Derivative [Line Items]
Derivative assets	1	1
Uranium | Other current liabilities
Derivative [Line Items]
Derivative liabilities	0	1
Union Electric Company
Derivative [Line Items]
Derivative assets	49	49
Derivative liabilities	68	77
Union Electric Company | Fuel oils | Other current assets
Derivative [Line Items]
Derivative assets	13	8
Union Electric Company | Fuel oils | Other assets
Derivative [Line Items]
Derivative assets	3	5
Union Electric Company | Natural gas | Other current assets
Derivative [Line Items]
Derivative assets	7	7
Union Electric Company | Natural gas | Other assets
Derivative [Line Items]
Derivative assets	9	5
Union Electric Company | Natural gas | Other current liabilities
Derivative [Line Items]
Derivative liabilities	7	2
Union Electric Company | Natural gas | Other deferred credits and liabilities
Derivative [Line Items]
Derivative liabilities	2	1
Union Electric Company | Power | Other current assets
Derivative [Line Items]
Derivative assets	14	23
Union Electric Company | Power | Other assets
Derivative [Line Items]
Derivative assets	0	0
Union Electric Company | Power | Other current liabilities
Derivative [Line Items]
Derivative liabilities	59	50
Union Electric Company | Power | Other deferred credits and liabilities
Derivative [Line Items]
Derivative liabilities	0	23
Union Electric Company | Uranium | Other current assets
Derivative [Line Items]
Derivative assets	2	0
Union Electric Company | Uranium | Other assets
Derivative [Line Items]
Derivative assets	1	1
Union Electric Company | Uranium | Other current liabilities
Derivative [Line Items]
Derivative liabilities	0	1
Ameren Illinois Company
Derivative [Line Items]
Derivative assets	40	41
Derivative liabilities	68	125
Ameren Illinois Company | Fuel oils | Other current assets
Derivative [Line Items]
Derivative assets	0	0
Ameren Illinois Company | Fuel oils | Other assets
Derivative [Line Items]
Derivative assets	0	0
Ameren Illinois Company | Natural gas | Other current assets
Derivative [Line Items]
Derivative assets	23	28
Ameren Illinois Company | Natural gas | Other assets
Derivative [Line Items]
Derivative assets	11	13
Ameren Illinois Company | Natural gas | Other current liabilities
Derivative [Line Items]
Derivative liabilities	20	6
Ameren Illinois Company | Natural gas | Other deferred credits and liabilities
Derivative [Line Items]
Derivative liabilities	9	2
Ameren Illinois Company | Power | Other current assets
Derivative [Line Items]
Derivative assets	2	0
Ameren Illinois Company | Power | Other assets
Derivative [Line Items]
Derivative assets	4	0
Ameren Illinois Company | Power | Other current liabilities
Derivative [Line Items]
Derivative liabilities	2	9
Ameren Illinois Company | Power | Other deferred credits and liabilities
Derivative [Line Items]
Derivative liabilities	37	108
Ameren Illinois Company | Uranium | Other current assets
Derivative [Line Items]
Derivative assets	0	0
Ameren Illinois Company | Uranium | Other assets
Derivative [Line Items]
Derivative assets	0	0
Ameren Illinois Company | Uranium | Other current liabilities
Derivative [Line Items]
Derivative liabilities	$ 0	$ 0