Derivative Financial Instruments (Derivative Instruments Carrying Value) (Details) - Not Designated As Hedging Instrument - USD ($) $ in Millions	Dec. 31, 2024	Dec. 31, 2023
Derivative [Line Items]
Derivative assets	$ 16	$ 22
Derivative liabilities	103	168
Fuel oils | Other current assets
Derivative [Line Items]
Derivative assets	0	2
Fuel oils | Other assets
Derivative [Line Items]
Derivative assets	0	0
Fuel oils | Other current liabilities
Derivative [Line Items]
Derivative liabilities	2	1
Fuel oils | Other deferred credits and liabilities
Derivative [Line Items]
Derivative liabilities	2	1
Natural gas | Other current assets
Derivative [Line Items]
Derivative assets	4	0
Natural gas | Other assets
Derivative [Line Items]
Derivative assets	6	6
Natural gas | Other current liabilities
Derivative [Line Items]
Derivative liabilities	27	57
Natural gas | Other deferred credits and liabilities
Derivative [Line Items]
Derivative liabilities	19	40
Power | Other current assets
Derivative [Line Items]
Derivative assets	6	5
Power | Other assets
Derivative [Line Items]
Derivative assets	0	0
Power | Other current liabilities
Derivative [Line Items]
Derivative liabilities	10	13
Power | Other deferred credits and liabilities
Derivative [Line Items]
Derivative liabilities	43	56
Uranium | Other current assets
Derivative [Line Items]
Derivative assets	0	9
Uranium | Other assets
Derivative [Line Items]
Derivative assets	0	0
Ameren Missouri
Derivative [Line Items]
Derivative assets	10	19
Derivative liabilities	15	25
Ameren Missouri | Fuel oils | Other current assets
Derivative [Line Items]
Derivative assets	0	2
Ameren Missouri | Fuel oils | Other assets
Derivative [Line Items]
Derivative assets	0	0
Ameren Missouri | Fuel oils | Other current liabilities
Derivative [Line Items]
Derivative liabilities	2	1
Ameren Missouri | Fuel oils | Other deferred credits and liabilities
Derivative [Line Items]
Derivative liabilities	2	1
Ameren Missouri | Natural gas | Other current assets
Derivative [Line Items]
Derivative assets	2	0
Ameren Missouri | Natural gas | Other assets
Derivative [Line Items]
Derivative assets	2	3
Ameren Missouri | Natural gas | Other current liabilities
Derivative [Line Items]
Derivative liabilities	5	12
Ameren Missouri | Natural gas | Other deferred credits and liabilities
Derivative [Line Items]
Derivative liabilities	6	10
Ameren Missouri | Power | Other current assets
Derivative [Line Items]
Derivative assets	6	5
Ameren Missouri | Power | Other assets
Derivative [Line Items]
Derivative assets	0	0
Ameren Missouri | Power | Other current liabilities
Derivative [Line Items]
Derivative liabilities	0	1
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	0	9
Ameren Missouri | Uranium | Other assets
Derivative [Line Items]
Derivative assets	0	0
Ameren Illinois
Derivative [Line Items]
Derivative assets	6	3
Derivative liabilities	88	143
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	2	0
Ameren Illinois | Natural gas | Other assets
Derivative [Line Items]
Derivative assets	4	3
Ameren Illinois | Natural gas | Other current liabilities
Derivative [Line Items]
Derivative liabilities	22	45
Ameren Illinois | Natural gas | Other deferred credits and liabilities
Derivative [Line Items]
Derivative liabilities	13	30
Ameren Illinois | Power | Other current assets
Derivative [Line Items]
Derivative assets	0	0
Ameren Illinois | Power | Other assets
Derivative [Line Items]
Derivative assets	0	0
Ameren Illinois | Power | Other current liabilities
Derivative [Line Items]
Derivative liabilities	10	12
Ameren Illinois | Power | Other deferred credits and liabilities
Derivative [Line Items]
Derivative liabilities	43	56
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