Segment Information (Disaggregation of Revenues) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Disaggregation of Revenue [Line Items]
External revenues	$ 7,957	$ 6,394	$ 5,794
Revenues from alternative revenue programs	78	77	36
Revenue Not from Contract with Customer, Other	(94)	68	36
Revenues	7,957	6,394	5,794
Union Electric Company
Disaggregation of Revenue [Line Items]
Revenues from alternative revenue programs	17	(16)	(14)
Revenue Not from Contract with Customer, Other	(103)	56	25
Ameren Illinois Electric Distribution
Disaggregation of Revenue [Line Items]
Revenues from alternative revenue programs	89	77	(20)
Revenue Not from Contract with Customer, Other	6	10	8
Ameren Illinois Gas
Disaggregation of Revenue [Line Items]
Revenues from alternative revenue programs	(19)	5	20
Revenue Not from Contract with Customer, Other	3	2	2
Ameren Transmission
Disaggregation of Revenue [Line Items]
Revenues from alternative revenue programs	(9)	11	50
Revenue Not from Contract with Customer, Other	0	0	1
Electric
Disaggregation of Revenue [Line Items]
External revenues	6,581	5,297	4,911
Revenues	6,581	5,297	4,911
Electric | Residential
Disaggregation of Revenue [Line Items]
External revenues	2,903	2,378	2,240
Electric | Commercial
Disaggregation of Revenue [Line Items]
External revenues	1,987	1,671	1,511
Electric | Industrial
Disaggregation of Revenue [Line Items]
External revenues	489	415	385
Electric | Other
Disaggregation of Revenue [Line Items]
Revenue Not from Contract with Customer	1,202	833	775
Natural gas
Disaggregation of Revenue [Line Items]
External revenues	1,376	1,097	883
Revenues	1,376	1,097	883
Natural gas | Residential
Disaggregation of Revenue [Line Items]
External revenues	965	736	617
Natural gas | Commercial
Disaggregation of Revenue [Line Items]
External revenues	277	206	165
Natural gas | Industrial
Disaggregation of Revenue [Line Items]
External revenues	48	39	18
Natural gas | Other
Disaggregation of Revenue [Line Items]
Revenue Not from Contract with Customer	86	116	83
Ameren Illinois Company
Disaggregation of Revenue [Line Items]
External revenues	3,756	2,895	2,535
Revenues from alternative revenue programs	63	91	42
Revenue Not from Contract with Customer, Other	9	12	10
Revenues	3,756	2,895	2,535
Ameren Illinois Company | Residential
Disaggregation of Revenue [Line Items]
External revenues	2,171	1,590	1,408
Ameren Illinois Company | Commercial
Disaggregation of Revenue [Line Items]
External revenues	989	717	622
Ameren Illinois Company | Industrial
Disaggregation of Revenue [Line Items]
External revenues	240	170	138
Ameren Illinois Company | Other
Disaggregation of Revenue [Line Items]
Revenue Not from Contract with Customer	356	418	367
Ameren Illinois Company | Ameren Illinois Electric Distribution
Disaggregation of Revenue [Line Items]
Revenues from alternative revenue programs	89	77	(20)
Revenue Not from Contract with Customer, Other	6	10	8
Ameren Illinois Company | Ameren Illinois Gas
Disaggregation of Revenue [Line Items]
Revenues from alternative revenue programs	(19)	5	20
Revenue Not from Contract with Customer, Other	3	2	2
Ameren Illinois Company | Ameren Illinois Transmission
Disaggregation of Revenue [Line Items]
Revenues from alternative revenue programs	(7)	9	42
Revenue Not from Contract with Customer, Other	0	0	0
Ameren Illinois Company | Electric
Disaggregation of Revenue [Line Items]
External revenues	2,576	1,938	1,775
Ameren Illinois Company | Natural gas
Disaggregation of Revenue [Line Items]
External revenues	1,180	957	760
Operating Segments | Union Electric Company
Disaggregation of Revenue [Line Items]
External revenues	4,012	3,311	3,069
Revenues	4,046	3,353	3,109
Operating Segments | Ameren Illinois Electric Distribution
Disaggregation of Revenue [Line Items]
External revenues	2,255	1,635	1,496
Revenues	2,256	1,639	1,498
Operating Segments | Ameren Illinois Gas
Disaggregation of Revenue [Line Items]
External revenues	1,180	957	760
Revenues	1,180	957	760
Operating Segments | Ameren Transmission
Disaggregation of Revenue [Line Items]
External revenues	510	491	469
Revenues	615	562	523
Operating Segments | Electric | Union Electric Company
Disaggregation of Revenue [Line Items]
Revenues	3,849	3,212	2,984
Operating Segments | Electric | Union Electric Company | Residential
Disaggregation of Revenue [Line Items]
External revenues	1,578	1,445	1,373
Operating Segments | Electric | Union Electric Company | Commercial
Disaggregation of Revenue [Line Items]
External revenues	1,219	1,126	1,025
Operating Segments | Electric | Union Electric Company | Industrial
Disaggregation of Revenue [Line Items]
External revenues	290	280	261
Operating Segments | Electric | Union Electric Company | Other
Disaggregation of Revenue [Line Items]
Revenue Not from Contract with Customer	762	361	325
Operating Segments | Electric | Ameren Illinois Electric Distribution
Disaggregation of Revenue [Line Items]
Revenues	2,256	1,639	1,498
Operating Segments | Electric | Ameren Illinois Electric Distribution | Residential
Disaggregation of Revenue [Line Items]
External revenues	1,325	933	867
Operating Segments | Electric | Ameren Illinois Electric Distribution | Commercial
Disaggregation of Revenue [Line Items]
External revenues	768	545	486
Operating Segments | Electric | Ameren Illinois Electric Distribution | Industrial
Disaggregation of Revenue [Line Items]
External revenues	199	135	124
Operating Segments | Electric | Ameren Illinois Electric Distribution | Other
Disaggregation of Revenue [Line Items]
Revenue Not from Contract with Customer	(36)	26	21
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	615	562	523
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	615	562	523
Operating Segments | Natural gas | Union Electric Company
Disaggregation of Revenue [Line Items]
Revenues	197	141	125
Operating Segments | Natural gas | Union Electric Company | Residential
Disaggregation of Revenue [Line Items]
External revenues	119	79	76
Operating Segments | Natural gas | Union Electric Company | Commercial
Disaggregation of Revenue [Line Items]
External revenues	56	34	29
Operating Segments | Natural gas | Union Electric Company | Industrial
Disaggregation of Revenue [Line Items]
External revenues	7	4	4
Operating Segments | Natural gas | Union Electric Company | Other
Disaggregation of Revenue [Line Items]
Revenue Not from Contract with Customer	15	24	16
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	1,180	957	760
Operating Segments | Natural gas | Ameren Illinois Gas | Residential
Disaggregation of Revenue [Line Items]
External revenues	846	657	541
Operating Segments | Natural gas | Ameren Illinois Gas | Commercial
Disaggregation of Revenue [Line Items]
External revenues	221	172	136
Operating Segments | Natural gas | Ameren Illinois Gas | Industrial
Disaggregation of Revenue [Line Items]
External revenues	41	35	14
Operating Segments | Natural gas | Ameren Illinois Gas | Other
Disaggregation of Revenue [Line Items]
Revenue Not from Contract with Customer	72	93	69
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 Company | Ameren Illinois Electric Distribution
Disaggregation of Revenue [Line Items]
External revenues	2,256	1,639	1,498
Operating Segments | Ameren Illinois Company | Ameren Illinois Gas
Disaggregation of Revenue [Line Items]
External revenues	1,180	957	760
Operating Segments | Ameren Illinois Company | Ameren Illinois Transmission
Disaggregation of Revenue [Line Items]
External revenues	320	299	277
Operating Segments | Ameren Illinois Company | Electric | Ameren Illinois Electric Distribution
Disaggregation of Revenue [Line Items]
Revenues	2,256	1,639	1,498
Operating Segments | Ameren Illinois Company | Electric | Ameren Illinois Electric Distribution | Residential
Disaggregation of Revenue [Line Items]
External revenues	1,325	933	867
Operating Segments | Ameren Illinois Company | Electric | Ameren Illinois Electric Distribution | Commercial
Disaggregation of Revenue [Line Items]
External revenues	768	545	486
Operating Segments | Ameren Illinois Company | Electric | Ameren Illinois Electric Distribution | Industrial
Disaggregation of Revenue [Line Items]
External revenues	199	135	124
Operating Segments | Ameren Illinois Company | Electric | Ameren Illinois Electric Distribution | Other
Disaggregation of Revenue [Line Items]
Revenue Not from Contract with Customer	(36)	26	21
Operating Segments | Ameren Illinois Company | Electric | Ameren Illinois Transmission
Disaggregation of Revenue [Line Items]
Revenues	424	365	329
Operating Segments | Ameren Illinois Company | Electric | Ameren Illinois Transmission | Residential
Disaggregation of Revenue [Line Items]
External revenues	0	0	0
Operating Segments | Ameren Illinois Company | Electric | Ameren Illinois Transmission | Commercial
Disaggregation of Revenue [Line Items]
External revenues	0	0	0
Operating Segments | Ameren Illinois Company | Electric | Ameren Illinois Transmission | Industrial
Disaggregation of Revenue [Line Items]
External revenues	0	0	0
Operating Segments | Ameren Illinois Company | Electric | Ameren Illinois Transmission | Other
Disaggregation of Revenue [Line Items]
Revenue Not from Contract with Customer	424	365	329
Operating Segments | Ameren Illinois Company | Natural gas | Ameren Illinois Gas
Disaggregation of Revenue [Line Items]
Revenues	1,180	957	760
Operating Segments | Ameren Illinois Company | Natural gas | Ameren Illinois Gas | Residential
Disaggregation of Revenue [Line Items]
External revenues	846	657	541
Operating Segments | Ameren Illinois Company | Natural gas | Ameren Illinois Gas | Commercial
Disaggregation of Revenue [Line Items]
External revenues	221	172	136
Operating Segments | Ameren Illinois Company | Natural gas | Ameren Illinois Gas | Industrial
Disaggregation of Revenue [Line Items]
External revenues	41	35	14
Operating Segments | Ameren Illinois Company | Natural gas | Ameren Illinois Gas | Other
Disaggregation of Revenue [Line Items]
Revenue Not from Contract with Customer	72	93	69
Intersegment Elimination
Disaggregation of Revenue [Line Items]
Revenue Not from Contract with Customer	(140)	(117)	(96)
Revenues	(140)	(117)	(96)
Intersegment Elimination | Union Electric Company
Disaggregation of Revenue [Line Items]
Revenue Not from Contract with Customer	(34)	(42)	(40)
Intersegment Elimination | Ameren Illinois Electric Distribution
Disaggregation of Revenue [Line Items]
Revenue Not from Contract with Customer	(1)	(4)	(2)
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	(105)	(71)	(54)
Intersegment Elimination | Electric
Disaggregation of Revenue [Line Items]
Revenues	(139)	(116)	(94)
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	(139)	(116)	(94)
Intersegment Elimination | Natural gas
Disaggregation of Revenue [Line Items]
Revenues	(1)	(1)	(2)
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)	(2)
Intersegment Elimination | Ameren Illinois Company
Disaggregation of Revenue [Line Items]
Revenue Not from Contract with Customer	(104)	(66)	(52)
Revenues	(104)	(66)	(52)
Intersegment Elimination | Ameren Illinois Company | Residential
Disaggregation of Revenue [Line Items]
External revenues	0	0	0
Intersegment Elimination | Ameren Illinois Company | Commercial
Disaggregation of Revenue [Line Items]
External revenues	0	0	0
Intersegment Elimination | Ameren Illinois Company | Industrial
Disaggregation of Revenue [Line Items]
External revenues	0	0	0
Intersegment Elimination | Ameren Illinois Company | Other
Disaggregation of Revenue [Line Items]
Revenue Not from Contract with Customer	(104)	(66)	(52)
Intersegment Elimination | Ameren Illinois Company | Ameren Illinois Electric Distribution
Disaggregation of Revenue [Line Items]
Revenue Not from Contract with Customer	0	0	0
Intersegment Elimination | Ameren Illinois Company | Ameren Illinois Gas
Disaggregation of Revenue [Line Items]
Revenue Not from Contract with Customer	0	0	0
Intersegment Elimination | Ameren Illinois Company | Ameren Illinois Transmission
Disaggregation of Revenue [Line Items]
Revenue Not from Contract with Customer	$ (104)	$ (66)	$ (52)