Derivative Financial Instruments (Derivative Instruments Carrying Value) (Details) - Not Designated As Hedging Instrument - USD ($) $ in Millions	Dec. 31, 2023	Dec. 31, 2022
Derivative [Line Items]
Derivative assets	$ 22	$ 89
Derivative liabilities	168	136
Fuel oils | Other current assets
Derivative [Line Items]
Derivative assets	2	13
Fuel oils | Other assets
Derivative [Line Items]
Derivative assets	0	3
Fuel oils | Other current liabilities
Derivative [Line Items]
Derivative liabilities	1	0
Fuel oils | Other deferred credits and liabilities
Derivative [Line Items]
Derivative liabilities	1	0
Natural gas | Other current assets
Derivative [Line Items]
Derivative assets	0	30
Natural gas | Other assets
Derivative [Line Items]
Derivative assets	6	20
Natural gas | Other current liabilities
Derivative [Line Items]
Derivative liabilities	57	27
Natural gas | Other deferred credits and liabilities
Derivative [Line Items]
Derivative liabilities	40	11
Power | Other current assets
Derivative [Line Items]
Derivative assets	5	16
Power | Other assets
Derivative [Line Items]
Derivative assets	0	4
Power | Other current liabilities
Derivative [Line Items]
Derivative liabilities	13	61
Power | Other deferred credits and liabilities
Derivative [Line Items]
Derivative liabilities	56	37
Uranium | Other current assets
Derivative [Line Items]
Derivative assets	9	2
Uranium | Other assets
Derivative [Line Items]
Derivative assets	0	1
Ameren Missouri
Derivative [Line Items]
Derivative assets	19	49
Derivative liabilities	25	68
Ameren Missouri | Fuel oils | Other current assets
Derivative [Line Items]
Derivative assets	2	13
Ameren Missouri | Fuel oils | Other assets
Derivative [Line Items]
Derivative assets	0	3
Ameren Missouri | Fuel oils | Other current liabilities
Derivative [Line Items]
Derivative liabilities	1	0
Ameren Missouri | Fuel oils | Other deferred credits and liabilities
Derivative [Line Items]
Derivative liabilities	1	0
Ameren Missouri | Natural gas | Other current assets
Derivative [Line Items]
Derivative assets	0	7
Ameren Missouri | Natural gas | Other assets
Derivative [Line Items]
Derivative assets	3	9
Ameren Missouri | Natural gas | Other current liabilities
Derivative [Line Items]
Derivative liabilities	12	7
Ameren Missouri | Natural gas | Other deferred credits and liabilities
Derivative [Line Items]
Derivative liabilities	10	2
Ameren Missouri | Power | Other current assets
Derivative [Line Items]
Derivative assets	5	14
Ameren Missouri | Power | Other assets
Derivative [Line Items]
Derivative assets	0	0
Ameren Missouri | Power | Other current liabilities
Derivative [Line Items]
Derivative liabilities	1	59
Ameren Missouri | Power | Other deferred credits and liabilities
Derivative [Line Items]
Derivative liabilities	0	0
Ameren Missouri | Uranium | Other current assets
Derivative [Line Items]
Derivative assets	9	2
Ameren Missouri | Uranium | Other assets
Derivative [Line Items]
Derivative assets	0	1
Ameren Illinois
Derivative [Line Items]
Derivative assets	3	40
Derivative liabilities	143	68
Ameren Illinois | Fuel oils | Other current assets
Derivative [Line Items]
Derivative assets	0	0
Ameren Illinois | Fuel oils | Other assets
Derivative [Line Items]
Derivative assets	0	0
Ameren Illinois | Fuel oils | Other current liabilities
Derivative [Line Items]
Derivative liabilities	0	0
Ameren Illinois | Fuel oils | Other deferred credits and liabilities
Derivative [Line Items]
Derivative liabilities	0	0
Ameren Illinois | Natural gas | Other current assets
Derivative [Line Items]
Derivative assets	0	23
Ameren Illinois | Natural gas | Other assets
Derivative [Line Items]
Derivative assets	3	11
Ameren Illinois | Natural gas | Other current liabilities
Derivative [Line Items]
Derivative liabilities	45	20
Ameren Illinois | Natural gas | Other deferred credits and liabilities
Derivative [Line Items]
Derivative liabilities	30	9
Ameren Illinois | Power | Other current assets
Derivative [Line Items]
Derivative assets	0	2
Ameren Illinois | Power | Other assets
Derivative [Line Items]
Derivative assets	0	4
Ameren Illinois | Power | Other current liabilities
Derivative [Line Items]
Derivative liabilities	12	2
Ameren Illinois | Power | Other deferred credits and liabilities
Derivative [Line Items]
Derivative liabilities	56	37
Ameren Illinois | Uranium | Other current assets
Derivative [Line Items]
Derivative assets	0	0
Ameren Illinois | Uranium | Other assets
Derivative [Line Items]
Derivative assets	$ 0	$ 0