Segment Information (Disaggregation of Revenues) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Disaggregation of Revenue [Line Items]
External revenues	$ 7,500	$ 7,957	$ 6,394
Revenues from alternative revenue programs	179	78	77
Revenue Not from Contract with Customer, Other	0	(94)	68
Revenues	7,500	7,957	6,394
Insurance recoveries related to lost sales		10	78
Ameren Missouri
Disaggregation of Revenue [Line Items]
Revenues from alternative revenue programs	(5)	17	(16)
Revenue Not from Contract with Customer, Other	(9)	(103)	56
Insurance recoveries related to lost sales		10	78
Ameren Illinois Electric Distribution
Disaggregation of Revenue [Line Items]
Revenues from alternative revenue programs	116	89	77
Revenue Not from Contract with Customer, Other	7	6	10
Ameren Illinois Gas
Disaggregation of Revenue [Line Items]
Revenues from alternative revenue programs	49	(19)	5
Revenue Not from Contract with Customer, Other	2	3	2
Ameren Transmission
Disaggregation of Revenue [Line Items]
Revenues from alternative revenue programs	19	(9)	11
Revenue Not from Contract with Customer, Other	0	0	0
Electric
Disaggregation of Revenue [Line Items]
External revenues	6,439	6,581	5,297
Revenues	6,439	6,581	5,297
Electric | Residential
Disaggregation of Revenue [Line Items]
External revenues	2,921	2,903	2,378
Electric | Commercial
Disaggregation of Revenue [Line Items]
External revenues	2,027	1,987	1,671
Electric | Industrial
Disaggregation of Revenue [Line Items]
External revenues	492	489	415
Electric | Other
Disaggregation of Revenue [Line Items]
Revenue Not from Contract with Customer	999	1,202	833
Natural gas
Disaggregation of Revenue [Line Items]
External revenues	1,061	1,376	1,097
Revenues	1,061	1,376	1,097
Natural gas | Residential
Disaggregation of Revenue [Line Items]
External revenues	757	965	736
Natural gas | Commercial
Disaggregation of Revenue [Line Items]
External revenues	210	277	206
Natural gas | Industrial
Disaggregation of Revenue [Line Items]
External revenues	19	48	39
Natural gas | Other
Disaggregation of Revenue [Line Items]
Revenue Not from Contract with Customer	75	86	116
Ameren Illinois
Disaggregation of Revenue [Line Items]
External revenues	3,482	3,756	2,895
Revenues from alternative revenue programs	177	63	91
Revenue Not from Contract with Customer, Other	9	9	12
Revenues	3,482	3,756	2,895
Ameren Illinois | Residential
Disaggregation of Revenue [Line Items]
External revenues	2,001	2,171	1,590
Ameren Illinois | Commercial
Disaggregation of Revenue [Line Items]
External revenues	911	989	717
Ameren Illinois | Industrial
Disaggregation of Revenue [Line Items]
External revenues	200	240	170
Ameren Illinois | Other
Disaggregation of Revenue [Line Items]
Revenue Not from Contract with Customer	370	356	418
Ameren Illinois | Ameren Illinois Electric Distribution
Disaggregation of Revenue [Line Items]
Revenues from alternative revenue programs	116	89	77
Revenue Not from Contract with Customer, Other	7	6	10
Ameren Illinois | Ameren Illinois Gas
Disaggregation of Revenue [Line Items]
Revenues from alternative revenue programs	49	(19)	5
Revenue Not from Contract with Customer, Other	2	3	2
Ameren Illinois | Ameren Illinois Transmission
Disaggregation of Revenue [Line Items]
Revenues from alternative revenue programs	12	(7)	9
Revenue Not from Contract with Customer, Other	0	0	0
Ameren Illinois | Electric
Disaggregation of Revenue [Line Items]
External revenues	2,585	2,576	1,938
Ameren Illinois | Natural gas
Disaggregation of Revenue [Line Items]
External revenues	897	1,180	957
Operating Segments | Ameren Missouri
Disaggregation of Revenue [Line Items]
External revenues	3,825	4,012	3,311
Revenues	3,859	4,046	3,353
Operating Segments | Ameren Illinois Electric Distribution
Disaggregation of Revenue [Line Items]
External revenues	2,217	2,255	1,635
Revenues	2,218	2,256	1,639
Operating Segments | Ameren Illinois Gas
Disaggregation of Revenue [Line Items]
External revenues	897	1,180	957
Revenues	897	1,180	957
Operating Segments | Ameren Transmission
Disaggregation of Revenue [Line Items]
External revenues	561	510	491
Revenues	677	615	562
Operating Segments | Electric | Ameren Missouri
Disaggregation of Revenue [Line Items]
Revenues	3,694	3,849	3,212
Operating Segments | Electric | Ameren Missouri | Residential
Disaggregation of Revenue [Line Items]
External revenues	1,577	1,578	1,445
Operating Segments | Electric | Ameren Missouri | Commercial
Disaggregation of Revenue [Line Items]
External revenues	1,280	1,219	1,126
Operating Segments | Electric | Ameren Missouri | Industrial
Disaggregation of Revenue [Line Items]
External revenues	306	290	280
Operating Segments | Electric | Ameren Missouri | Other
Disaggregation of Revenue [Line Items]
Revenue Not from Contract with Customer	531	762	361
Operating Segments | Electric | Ameren Illinois Electric Distribution
Disaggregation of Revenue [Line Items]
Revenues	2,218	2,256	1,639
Operating Segments | Electric | Ameren Illinois Electric Distribution | Residential
Disaggregation of Revenue [Line Items]
External revenues	1,344	1,325	933
Operating Segments | Electric | Ameren Illinois Electric Distribution | Commercial
Disaggregation of Revenue [Line Items]
External revenues	747	768	545
Operating Segments | Electric | Ameren Illinois Electric Distribution | Industrial
Disaggregation of Revenue [Line Items]
External revenues	186	199	135
Operating Segments | Electric | Ameren Illinois Electric Distribution | Other
Disaggregation of Revenue [Line Items]
Revenue Not from Contract with Customer	(59)	(36)	26
Operating Segments | Electric | Ameren Illinois Gas
Disaggregation of Revenue [Line Items]
Revenues	0	0	0
Operating Segments | Electric | Ameren Illinois Gas | Residential
Disaggregation of Revenue [Line Items]
External revenues	0	0	0
Operating Segments | Electric | Ameren Illinois Gas | Commercial
Disaggregation of Revenue [Line Items]
External revenues	0	0	0
Operating Segments | Electric | Ameren Illinois Gas | Industrial
Disaggregation of Revenue [Line Items]
External revenues	0	0	0
Operating Segments | Electric | Ameren Illinois Gas | Other
Disaggregation of Revenue [Line Items]
Revenue Not from Contract with Customer	0	0	0
Operating Segments | Electric | Ameren Transmission
Disaggregation of Revenue [Line Items]
Revenues	677	615	562
Operating Segments | Electric | Ameren Transmission | Residential
Disaggregation of Revenue [Line Items]
External revenues	0	0	0
Operating Segments | Electric | Ameren Transmission | Commercial
Disaggregation of Revenue [Line Items]
External revenues	0	0	0
Operating Segments | Electric | Ameren Transmission | Industrial
Disaggregation of Revenue [Line Items]
External revenues	0	0	0
Operating Segments | Electric | Ameren Transmission | Other
Disaggregation of Revenue [Line Items]
Revenue Not from Contract with Customer	677	615	562
Operating Segments | Natural gas | Ameren Missouri
Disaggregation of Revenue [Line Items]
Revenues	165	197	141
Operating Segments | Natural gas | Ameren Missouri | Residential
Disaggregation of Revenue [Line Items]
External revenues	100	119	79
Operating Segments | Natural gas | Ameren Missouri | Commercial
Disaggregation of Revenue [Line Items]
External revenues	46	56	34
Operating Segments | Natural gas | Ameren Missouri | Industrial
Disaggregation of Revenue [Line Items]
External revenues	5	7	4
Operating Segments | Natural gas | Ameren Missouri | Other
Disaggregation of Revenue [Line Items]
Revenue Not from Contract with Customer	14	15	24
Operating Segments | Natural gas | Ameren Illinois Electric Distribution
Disaggregation of Revenue [Line Items]
Revenues	0	0	0
Operating Segments | Natural gas | Ameren Illinois Electric Distribution | Residential
Disaggregation of Revenue [Line Items]
External revenues	0	0	0
Operating Segments | Natural gas | Ameren Illinois Electric Distribution | Commercial
Disaggregation of Revenue [Line Items]
External revenues	0	0	0
Operating Segments | Natural gas | Ameren Illinois Electric Distribution | Industrial
Disaggregation of Revenue [Line Items]
External revenues	0	0	0
Operating Segments | Natural gas | Ameren Illinois Electric Distribution | Other
Disaggregation of Revenue [Line Items]
Revenue Not from Contract with Customer	0	0	0
Operating Segments | Natural gas | Ameren Illinois Gas
Disaggregation of Revenue [Line Items]
Revenues	897	1,180	957
Operating Segments | Natural gas | Ameren Illinois Gas | Residential
Disaggregation of Revenue [Line Items]
External revenues	657	846	657
Operating Segments | Natural gas | Ameren Illinois Gas | Commercial
Disaggregation of Revenue [Line Items]
External revenues	164	221	172
Operating Segments | Natural gas | Ameren Illinois Gas | Industrial
Disaggregation of Revenue [Line Items]
External revenues	14	41	35
Operating Segments | Natural gas | Ameren Illinois Gas | Other
Disaggregation of Revenue [Line Items]
Revenue Not from Contract with Customer	62	72	93
Operating Segments | Natural gas | Ameren Transmission
Disaggregation of Revenue [Line Items]
Revenues	0	0	0
Operating Segments | Natural gas | Ameren Transmission | Residential
Disaggregation of Revenue [Line Items]
External revenues	0	0	0
Operating Segments | Natural gas | Ameren Transmission | Commercial
Disaggregation of Revenue [Line Items]
External revenues	0	0	0
Operating Segments | Natural gas | Ameren Transmission | Industrial
Disaggregation of Revenue [Line Items]
External revenues	0	0	0
Operating Segments | Natural gas | Ameren Transmission | Other
Disaggregation of Revenue [Line Items]
Revenue Not from Contract with Customer	0	0	0
Operating Segments | Ameren Illinois | Ameren Illinois Electric Distribution
Disaggregation of Revenue [Line Items]
External revenues	2,218	2,256	1,639
Operating Segments | Ameren Illinois | Ameren Illinois Gas
Disaggregation of Revenue [Line Items]
External revenues	897	1,180	957
Operating Segments | Ameren Illinois | Ameren Illinois Transmission
Disaggregation of Revenue [Line Items]
External revenues	367	320	299
Operating Segments | Ameren Illinois | Electric | Ameren Illinois Electric Distribution
Disaggregation of Revenue [Line Items]
Revenues	2,218	2,256	1,639
Operating Segments | Ameren Illinois | Electric | Ameren Illinois Electric Distribution | Residential
Disaggregation of Revenue [Line Items]
External revenues	1,344	1,325	933
Operating Segments | Ameren Illinois | Electric | Ameren Illinois Electric Distribution | Commercial
Disaggregation of Revenue [Line Items]
External revenues	747	768	545
Operating Segments | Ameren Illinois | Electric | Ameren Illinois Electric Distribution | Industrial
Disaggregation of Revenue [Line Items]
External revenues	186	199	135
Operating Segments | Ameren Illinois | Electric | Ameren Illinois Electric Distribution | Other
Disaggregation of Revenue [Line Items]
Revenue Not from Contract with Customer	(59)	(36)	26
Operating Segments | Ameren Illinois | Electric | Ameren Illinois Transmission
Disaggregation of Revenue [Line Items]
Revenues	480	424	365
Operating Segments | Ameren Illinois | Electric | Ameren Illinois Transmission | Residential
Disaggregation of Revenue [Line Items]
External revenues	0	0	0
Operating Segments | Ameren Illinois | Electric | Ameren Illinois Transmission | Commercial
Disaggregation of Revenue [Line Items]
External revenues	0	0	0
Operating Segments | Ameren Illinois | Electric | Ameren Illinois Transmission | Industrial
Disaggregation of Revenue [Line Items]
External revenues	0	0	0
Operating Segments | Ameren Illinois | Electric | Ameren Illinois Transmission | Other
Disaggregation of Revenue [Line Items]
Revenue Not from Contract with Customer	480	424	365
Operating Segments | Ameren Illinois | Natural gas | Ameren Illinois Gas
Disaggregation of Revenue [Line Items]
Revenues	897	1,180	957
Operating Segments | Ameren Illinois | Natural gas | Ameren Illinois Gas | Residential
Disaggregation of Revenue [Line Items]
External revenues	657	846	657
Operating Segments | Ameren Illinois | Natural gas | Ameren Illinois Gas | Commercial
Disaggregation of Revenue [Line Items]
External revenues	164	221	172
Operating Segments | Ameren Illinois | Natural gas | Ameren Illinois Gas | Industrial
Disaggregation of Revenue [Line Items]
External revenues	14	41	35
Operating Segments | Ameren Illinois | Natural gas | Ameren Illinois Gas | Other
Disaggregation of Revenue [Line Items]
Revenue Not from Contract with Customer	62	72	93
Intersegment Elimination
Disaggregation of Revenue [Line Items]
Revenue Not from Contract with Customer	(151)	(140)	(117)
Revenues	(151)	(140)	(117)
Intersegment Elimination | Ameren Missouri
Disaggregation of Revenue [Line Items]
Revenue Not from Contract with Customer	(34)	(34)	(42)
Intersegment Elimination | Ameren Illinois Electric Distribution
Disaggregation of Revenue [Line Items]
Revenue Not from Contract with Customer	(1)	(1)	(4)
Intersegment Elimination | Ameren Illinois Gas
Disaggregation of Revenue [Line Items]
Revenue Not from Contract with Customer	0	0	0
Intersegment Elimination | Ameren Transmission
Disaggregation of Revenue [Line Items]
Revenue Not from Contract with Customer	(116)	(105)	(71)
Intersegment Elimination | Electric
Disaggregation of Revenue [Line Items]
Revenues	(150)	(139)	(116)
Intersegment Elimination | Electric | Residential
Disaggregation of Revenue [Line Items]
External revenues	0	0	0
Intersegment Elimination | Electric | Commercial
Disaggregation of Revenue [Line Items]
External revenues	0	0	0
Intersegment Elimination | Electric | Industrial
Disaggregation of Revenue [Line Items]
External revenues	0	0	0
Intersegment Elimination | Electric | Other
Disaggregation of Revenue [Line Items]
Revenue Not from Contract with Customer	(150)	(139)	(116)
Intersegment Elimination | Natural gas
Disaggregation of Revenue [Line Items]
Revenues	(1)	(1)	(1)
Intersegment Elimination | Natural gas | Residential
Disaggregation of Revenue [Line Items]
External revenues	0	0	0
Intersegment Elimination | Natural gas | Commercial
Disaggregation of Revenue [Line Items]
External revenues	0	0	0
Intersegment Elimination | Natural gas | Industrial
Disaggregation of Revenue [Line Items]
External revenues	0	0	0
Intersegment Elimination | Natural gas | Other
Disaggregation of Revenue [Line Items]
Revenue Not from Contract with Customer	(1)	(1)	(1)
Intersegment Elimination | Ameren Illinois
Disaggregation of Revenue [Line Items]
Revenue Not from Contract with Customer	(113)	(104)	(66)
Revenues	(113)	(104)	(66)
Intersegment Elimination | Ameren Illinois | Residential
Disaggregation of Revenue [Line Items]
External revenues	0	0	0
Intersegment Elimination | Ameren Illinois | Commercial
Disaggregation of Revenue [Line Items]
External revenues	0	0	0
Intersegment Elimination | Ameren Illinois | Industrial
Disaggregation of Revenue [Line Items]
External revenues	0	0	0
Intersegment Elimination | Ameren Illinois | Other
Disaggregation of Revenue [Line Items]
Revenue Not from Contract with Customer	(113)	(104)	(66)
Intersegment Elimination | Ameren Illinois | Ameren Illinois Electric Distribution
Disaggregation of Revenue [Line Items]
Revenue Not from Contract with Customer	0	0	0
Intersegment Elimination | Ameren Illinois | Ameren Illinois Gas
Disaggregation of Revenue [Line Items]
Revenue Not from Contract with Customer	0	0	0
Intersegment Elimination | Ameren Illinois | Ameren Illinois Transmission
Disaggregation of Revenue [Line Items]
Revenue Not from Contract with Customer	$ (113)	$ (104)	$ (66)