Segment Information (Disaggregation of Revenue) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2023	Mar. 31, 2022
Disaggregation of Revenue [Line Items]
Revenues	$ 2,062	$ 1,879
Revenues	2,062	1,879
Revenues from alternative revenue programs	98	45
Other revenues not from contracts with customers	(3)	3
Union Electric Company
Disaggregation of Revenue [Line Items]
Revenues from alternative revenue programs	(2)	(6)
Other revenues not from contracts with customers	(6)	0
Ameren Illinois Electric Distribution
Disaggregation of Revenue [Line Items]
Revenues from alternative revenue programs	64	55
Other revenues not from contracts with customers	2	2
Ameren Illinois Natural Gas
Disaggregation of Revenue [Line Items]
Revenues from alternative revenue programs	28	(5)
Other revenues not from contracts with customers	1	1
Ameren Transmission
Disaggregation of Revenue [Line Items]
Revenues from alternative revenue programs	8	1
Other revenues not from contracts with customers	0	0
Electric
Disaggregation of Revenue [Line Items]
Revenues	1,590	1,318
Revenues	1,590	1,318
Electric | Residential
Disaggregation of Revenue [Line Items]
Revenues	706	595
Electric | Commercial
Disaggregation of Revenue [Line Items]
Revenues	447	398
Electric | Industrial
Disaggregation of Revenue [Line Items]
Revenues	109	102
Electric | Other
Disaggregation of Revenue [Line Items]
Revenues	328	223
Natural gas
Disaggregation of Revenue [Line Items]
Revenues	472	561
Revenues	472	561
Natural gas | Residential
Disaggregation of Revenue [Line Items]
Revenues	348	420
Natural gas | Commercial
Disaggregation of Revenue [Line Items]
Revenues	100	119
Natural gas | Industrial
Disaggregation of Revenue [Line Items]
Revenues	9	19
Natural gas | Other
Disaggregation of Revenue [Line Items]
Revenues	15	3
Ameren Illinois Company
Disaggregation of Revenue [Line Items]
Revenues	1,101	1,024
Revenues	1,101	1,024
Revenues from alternative revenue programs	99	51
Other revenues not from contracts with customers	3	3
Ameren Illinois Company | Residential
Disaggregation of Revenue [Line Items]
Revenues	678	632
Ameren Illinois Company | Commercial
Disaggregation of Revenue [Line Items]
Revenues	277	255
Ameren Illinois Company | Industrial
Disaggregation of Revenue [Line Items]
Revenues	55	62
Ameren Illinois Company | Other
Disaggregation of Revenue [Line Items]
Revenues	91	75
Ameren Illinois Company | Ameren Illinois Electric Distribution
Disaggregation of Revenue [Line Items]
Revenues from alternative revenue programs	64	55
Other revenues not from contracts with customers	2	2
Ameren Illinois Company | Ameren Illinois Natural Gas
Disaggregation of Revenue [Line Items]
Revenues from alternative revenue programs	28	(5)
Other revenues not from contracts with customers	1	1
Ameren Illinois Company | Ameren Illinois Transmission
Disaggregation of Revenue [Line Items]
Revenues from alternative revenue programs	7	1
Other revenues not from contracts with customers	0	0
Ameren Illinois Company | Electric
Disaggregation of Revenue [Line Items]
Revenues	710	543
Ameren Illinois Company | Natural gas
Disaggregation of Revenue [Line Items]
Revenues	391	481
Operating Segments | Union Electric Company
Disaggregation of Revenue [Line Items]
Revenues	913	808
Revenues	923	818
Operating Segments | Ameren Illinois Electric Distribution
Disaggregation of Revenue [Line Items]
Revenues	624	464
Revenues	624	465
Operating Segments | Ameren Illinois Natural Gas
Disaggregation of Revenue [Line Items]
Revenues	391	481
Revenues	391	481
Operating Segments | Ameren Transmission
Disaggregation of Revenue [Line Items]
Revenues	134	126
Revenues	163	146
Operating Segments | Electric | Union Electric Company
Disaggregation of Revenue [Line Items]
Revenues	841	738
Operating Segments | Electric | Union Electric Company | Residential
Disaggregation of Revenue [Line Items]
Revenues	324	332
Operating Segments | Electric | Union Electric Company | Commercial
Disaggregation of Revenue [Line Items]
Revenues	247	240
Operating Segments | Electric | Union Electric Company | Industrial
Disaggregation of Revenue [Line Items]
Revenues	61	57
Operating Segments | Electric | Union Electric Company | Other
Disaggregation of Revenue [Line Items]
Revenues	209	109
Operating Segments | Electric | Ameren Illinois Electric Distribution
Disaggregation of Revenue [Line Items]
Revenues	624	465
Operating Segments | Electric | Ameren Illinois Electric Distribution | Residential
Disaggregation of Revenue [Line Items]
Revenues	382	263
Operating Segments | Electric | Ameren Illinois Electric Distribution | Commercial
Disaggregation of Revenue [Line Items]
Revenues	200	158
Operating Segments | Electric | Ameren Illinois Electric Distribution | Industrial
Disaggregation of Revenue [Line Items]
Revenues	48	45
Operating Segments | Electric | Ameren Illinois Electric Distribution | Other
Disaggregation of Revenue [Line Items]
Revenues	(6)	(1)
Operating Segments | Electric | Ameren Illinois Natural Gas
Disaggregation of Revenue [Line Items]
Revenues	0	0
Operating Segments | Electric | Ameren Illinois Natural Gas | Residential
Disaggregation of Revenue [Line Items]
Revenues	0	0
Operating Segments | Electric | Ameren Illinois Natural Gas | Commercial
Disaggregation of Revenue [Line Items]
Revenues	0	0
Operating Segments | Electric | Ameren Illinois Natural Gas | Industrial
Disaggregation of Revenue [Line Items]
Revenues	0	0
Operating Segments | Electric | Ameren Illinois Natural Gas | Other
Disaggregation of Revenue [Line Items]
Revenues	0	0
Operating Segments | Electric | Ameren Transmission
Disaggregation of Revenue [Line Items]
Revenues	163	146
Operating Segments | Electric | Ameren Transmission | Residential
Disaggregation of Revenue [Line Items]
Revenues	0	0
Operating Segments | Electric | Ameren Transmission | Commercial
Disaggregation of Revenue [Line Items]
Revenues	0	0
Operating Segments | Electric | Ameren Transmission | Industrial
Disaggregation of Revenue [Line Items]
Revenues	0	0
Operating Segments | Electric | Ameren Transmission | Other
Disaggregation of Revenue [Line Items]
Revenues	163	146
Operating Segments | Natural gas | Union Electric Company
Disaggregation of Revenue [Line Items]
Revenues	82	80
Operating Segments | Natural gas | Union Electric Company | Residential
Disaggregation of Revenue [Line Items]
Revenues	52	51
Operating Segments | Natural gas | Union Electric Company | Commercial
Disaggregation of Revenue [Line Items]
Revenues	23	22
Operating Segments | Natural gas | Union Electric Company | Industrial
Disaggregation of Revenue [Line Items]
Revenues	2	2
Operating Segments | Natural gas | Union Electric Company | Other
Disaggregation of Revenue [Line Items]
Revenues	5	5
Operating Segments | Natural gas | Ameren Illinois Electric Distribution
Disaggregation of Revenue [Line Items]
Revenues	0	0
Operating Segments | Natural gas | Ameren Illinois Electric Distribution | Residential
Disaggregation of Revenue [Line Items]
Revenues	0	0
Operating Segments | Natural gas | Ameren Illinois Electric Distribution | Commercial
Disaggregation of Revenue [Line Items]
Revenues	0	0
Operating Segments | Natural gas | Ameren Illinois Electric Distribution | Industrial
Disaggregation of Revenue [Line Items]
Revenues	0	0
Operating Segments | Natural gas | Ameren Illinois Electric Distribution | Other
Disaggregation of Revenue [Line Items]
Revenues	0	0
Operating Segments | Natural gas | Ameren Illinois Natural Gas
Disaggregation of Revenue [Line Items]
Revenues	391	481
Operating Segments | Natural gas | Ameren Illinois Natural Gas | Residential
Disaggregation of Revenue [Line Items]
Revenues	296	369
Operating Segments | Natural gas | Ameren Illinois Natural Gas | Commercial
Disaggregation of Revenue [Line Items]
Revenues	77	97
Operating Segments | Natural gas | Ameren Illinois Natural Gas | Industrial
Disaggregation of Revenue [Line Items]
Revenues	7	17
Operating Segments | Natural gas | Ameren Illinois Natural Gas | Other
Disaggregation of Revenue [Line Items]
Revenues	11	(2)
Operating Segments | Natural gas | Ameren Transmission
Disaggregation of Revenue [Line Items]
Revenues	0	0
Operating Segments | Natural gas | Ameren Transmission | Residential
Disaggregation of Revenue [Line Items]
Revenues	0	0
Operating Segments | Natural gas | Ameren Transmission | Commercial
Disaggregation of Revenue [Line Items]
Revenues	0	0
Operating Segments | Natural gas | Ameren Transmission | Industrial
Disaggregation of Revenue [Line Items]
Revenues	0	0
Operating Segments | Natural gas | Ameren Transmission | Other
Disaggregation of Revenue [Line Items]
Revenues	0	0
Operating Segments | Ameren Illinois Company | Ameren Illinois Electric Distribution
Disaggregation of Revenue [Line Items]
Revenues	624	465
Operating Segments | Ameren Illinois Company | Ameren Illinois Natural Gas
Disaggregation of Revenue [Line Items]
Revenues	391	481
Operating Segments | Ameren Illinois Company | Ameren Illinois Transmission
Disaggregation of Revenue [Line Items]
Revenues	86	78
Operating Segments | Ameren Illinois Company | Electric | Ameren Illinois Electric Distribution
Disaggregation of Revenue [Line Items]
Revenues	624	465
Operating Segments | Ameren Illinois Company | Electric | Ameren Illinois Electric Distribution | Residential
Disaggregation of Revenue [Line Items]
Revenues	382	263
Operating Segments | Ameren Illinois Company | Electric | Ameren Illinois Electric Distribution | Commercial
Disaggregation of Revenue [Line Items]
Revenues	200	158
Operating Segments | Ameren Illinois Company | Electric | Ameren Illinois Electric Distribution | Industrial
Disaggregation of Revenue [Line Items]
Revenues	48	45
Operating Segments | Ameren Illinois Company | Electric | Ameren Illinois Electric Distribution | Other
Disaggregation of Revenue [Line Items]
Revenues	(6)	(1)
Operating Segments | Ameren Illinois Company | Electric | Ameren Illinois Transmission
Disaggregation of Revenue [Line Items]
Revenues	114	98
Operating Segments | Ameren Illinois Company | Electric | Ameren Illinois Transmission | Residential
Disaggregation of Revenue [Line Items]
Revenues	0	0
Operating Segments | Ameren Illinois Company | Electric | Ameren Illinois Transmission | Commercial
Disaggregation of Revenue [Line Items]
Revenues	0	0
Operating Segments | Ameren Illinois Company | Electric | Ameren Illinois Transmission | Industrial
Disaggregation of Revenue [Line Items]
Revenues	0	0
Operating Segments | Ameren Illinois Company | Electric | Ameren Illinois Transmission | Other
Disaggregation of Revenue [Line Items]
Revenues	114	98
Operating Segments | Ameren Illinois Company | Natural gas | Ameren Illinois Natural Gas
Disaggregation of Revenue [Line Items]
Revenues	391	481
Operating Segments | Ameren Illinois Company | Natural gas | Ameren Illinois Natural Gas | Residential
Disaggregation of Revenue [Line Items]
Revenues	296	369
Operating Segments | Ameren Illinois Company | Natural gas | Ameren Illinois Natural Gas | Commercial
Disaggregation of Revenue [Line Items]
Revenues	77	97
Operating Segments | Ameren Illinois Company | Natural gas | Ameren Illinois Natural Gas | Industrial
Disaggregation of Revenue [Line Items]
Revenues	7	17
Operating Segments | Ameren Illinois Company | Natural gas | Ameren Illinois Natural Gas | Other
Disaggregation of Revenue [Line Items]
Revenues	11	(2)
Intersegment Eliminations
Disaggregation of Revenue [Line Items]
Revenues	(39)	(31)
Revenues	(39)	(31)
Intersegment Eliminations | Union Electric Company
Disaggregation of Revenue [Line Items]
Revenues	(10)	(10)
Intersegment Eliminations | Ameren Illinois Electric Distribution
Disaggregation of Revenue [Line Items]
Revenues	0	(1)
Intersegment Eliminations | Ameren Illinois Natural Gas
Disaggregation of Revenue [Line Items]
Revenues	0	0
Intersegment Eliminations | Ameren Transmission
Disaggregation of Revenue [Line Items]
Revenues	(29)	(20)
Intersegment Eliminations | Electric
Disaggregation of Revenue [Line Items]
Revenues	(38)	(31)
Intersegment Eliminations | Electric | Residential
Disaggregation of Revenue [Line Items]
Revenues	0	0
Intersegment Eliminations | Electric | Commercial
Disaggregation of Revenue [Line Items]
Revenues	0	0
Intersegment Eliminations | Electric | Industrial
Disaggregation of Revenue [Line Items]
Revenues	0	0
Intersegment Eliminations | Electric | Other
Disaggregation of Revenue [Line Items]
Revenues	(38)	(31)
Intersegment Eliminations | Natural gas
Disaggregation of Revenue [Line Items]
Revenues	(1)	0
Intersegment Eliminations | Natural gas | Residential
Disaggregation of Revenue [Line Items]
Revenues	0	0
Intersegment Eliminations | Natural gas | Commercial
Disaggregation of Revenue [Line Items]
Revenues	0	0
Intersegment Eliminations | Natural gas | Industrial
Disaggregation of Revenue [Line Items]
Revenues	0	0
Intersegment Eliminations | Natural gas | Other
Disaggregation of Revenue [Line Items]
Revenues	(1)	0
Intersegment Eliminations | Ameren Illinois Company
Disaggregation of Revenue [Line Items]
Revenues	(28)	(20)
Revenues	(28)	(20)
Intersegment Eliminations | Ameren Illinois Company | Residential
Disaggregation of Revenue [Line Items]
Revenues	0	0
Intersegment Eliminations | Ameren Illinois Company | Commercial
Disaggregation of Revenue [Line Items]
Revenues	0	0
Intersegment Eliminations | Ameren Illinois Company | Industrial
Disaggregation of Revenue [Line Items]
Revenues	0	0
Intersegment Eliminations | Ameren Illinois Company | Other
Disaggregation of Revenue [Line Items]
Revenues	(28)	(20)
Intersegment Eliminations | Ameren Illinois Company | Ameren Illinois Electric Distribution
Disaggregation of Revenue [Line Items]
Revenues	0	0
Intersegment Eliminations | Ameren Illinois Company | Ameren Illinois Natural Gas
Disaggregation of Revenue [Line Items]
Revenues	0	0
Intersegment Eliminations | Ameren Illinois Company | Ameren Illinois Transmission
Disaggregation of Revenue [Line Items]
Revenues	$ (28)	$ (20)