Segment Information (Disaggregation of Revenue) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2024	Sep. 30, 2023
Disaggregation of Revenue [Line Items]
Operating Revenues	$ 2,173	$ 2,060	$ 5,682	$ 5,882
Revenues	2,173	2,060	5,682	5,882
Revenues from alternative revenue programs	(155)	(109)	(69)	63
Other revenues not from contracts with customers	4	1	11	(1)
Union Electric Company
Disaggregation of Revenue [Line Items]
Revenues from alternative revenue programs	0	(9)	(7)	(11)
Other revenues not from contracts with customers	2	(1)	4	(9)
Ameren Illinois Electric Distribution
Disaggregation of Revenue [Line Items]
Revenues from alternative revenue programs	(144)	(94)	(83)	30
Other revenues not from contracts with customers	2	2	5	6
Ameren Illinois Natural Gas
Disaggregation of Revenue [Line Items]
Revenues from alternative revenue programs	(9)	(1)	10	36
Other revenues not from contracts with customers	0	0	2	2
Ameren Transmission
Disaggregation of Revenue [Line Items]
Revenues from alternative revenue programs	(2)	(5)	11	8
Other revenues not from contracts with customers	0	0	0	0
Electric
Disaggregation of Revenue [Line Items]
Operating Revenues	2,035	1,921	4,920	5,096
Revenues	2,035	1,921	4,920	5,096
Electric | Residential
Disaggregation of Revenue [Line Items]
Operating Revenues	929	920	2,273	2,323
Electric | Commercial
Disaggregation of Revenue [Line Items]
Operating Revenues	649	657	1,560	1,608
Electric | Industrial
Disaggregation of Revenue [Line Items]
Operating Revenues	146	147	376	379
Electric | Other
Disaggregation of Revenue [Line Items]
Revenues	311	197	711	786
Natural gas
Disaggregation of Revenue [Line Items]
Operating Revenues	138	139	762	786
Revenues	138	139	762	786
Natural gas | Residential
Disaggregation of Revenue [Line Items]
Operating Revenues	86	84	528	543
Natural gas | Commercial
Disaggregation of Revenue [Line Items]
Operating Revenues	24	24	137	155
Natural gas | Industrial
Disaggregation of Revenue [Line Items]
Operating Revenues	2	2	10	14
Natural gas | Other
Disaggregation of Revenue [Line Items]
Revenues	26	29	87	74
Ameren Illinois Company
Disaggregation of Revenue [Line Items]
Operating Revenues	793	783	2,559	2,663
Revenues	793	783	2,559	2,663
Revenues from alternative revenue programs	(154)	(101)	(64)	70
Other revenues not from contracts with customers	2	2	7	8
Ameren Illinois Company | Residential
Disaggregation of Revenue [Line Items]
Operating Revenues	416	405	1,413	1,518
Ameren Illinois Company | Commercial
Disaggregation of Revenue [Line Items]
Operating Revenues	203	208	623	703
Ameren Illinois Company | Industrial
Disaggregation of Revenue [Line Items]
Operating Revenues	40	41	137	146
Ameren Illinois Company | Other
Disaggregation of Revenue [Line Items]
Revenues	134	129	386	296
Ameren Illinois Company | Ameren Illinois Electric Distribution
Disaggregation of Revenue [Line Items]
Revenues from alternative revenue programs	(144)	(94)	(83)	30
Other revenues not from contracts with customers	2	2	5	6
Ameren Illinois Company | Ameren Illinois Natural Gas
Disaggregation of Revenue [Line Items]
Revenues from alternative revenue programs	(9)	(1)	10	36
Other revenues not from contracts with customers	0	0	2	2
Ameren Illinois Company | Ameren Illinois Transmission
Disaggregation of Revenue [Line Items]
Revenues from alternative revenue programs	(1)	(6)	9	4
Other revenues not from contracts with customers	0	0	0	0
Ameren Illinois Company | Electric
Disaggregation of Revenue [Line Items]
Operating Revenues	672	661	1,899	1,998
Ameren Illinois Company | Natural gas
Disaggregation of Revenue [Line Items]
Operating Revenues	121	122	660	665
Operating Segments | Union Electric Company
Disaggregation of Revenue [Line Items]
Operating Revenues	1,333	1,228	2,980	3,074
Revenues	1,342	1,237	3,005	3,101
Operating Segments | Ameren Illinois Electric Distribution
Disaggregation of Revenue [Line Items]
Operating Revenues	551	557	1,566	1,721
Revenues	552	558	1,567	1,722
Operating Segments | Ameren Illinois Natural Gas
Disaggregation of Revenue [Line Items]
Operating Revenues	121	121	660	664
Revenues	121	122	660	665
Operating Segments | Ameren Transmission
Disaggregation of Revenue [Line Items]
Operating Revenues	168	154	476	423
Revenues	210	188	586	512
Operating Segments | Electric | Union Electric Company
Disaggregation of Revenue [Line Items]
Revenues	1,324	1,219	2,902	2,978
Operating Segments | Electric | Union Electric Company | Residential
Disaggregation of Revenue [Line Items]
Operating Revenues	590	590	1,326	1,274
Operating Segments | Electric | Union Electric Company | Commercial
Disaggregation of Revenue [Line Items]
Operating Revenues	465	468	1,048	1,026
Operating Segments | Electric | Union Electric Company | Industrial
Disaggregation of Revenue [Line Items]
Operating Revenues	108	107	246	243
Operating Segments | Electric | Union Electric Company | Other
Disaggregation of Revenue [Line Items]
Revenues	161	54	282	435
Operating Segments | Electric | Ameren Illinois Electric Distribution
Disaggregation of Revenue [Line Items]
Revenues	552	558	1,567	1,722
Operating Segments | Electric | Ameren Illinois Electric Distribution | Residential
Disaggregation of Revenue [Line Items]
Operating Revenues	339	330	947	1,049
Operating Segments | Electric | Ameren Illinois Electric Distribution | Commercial
Disaggregation of Revenue [Line Items]
Operating Revenues	184	189	512	582
Operating Segments | Electric | Ameren Illinois Electric Distribution | Industrial
Disaggregation of Revenue [Line Items]
Operating Revenues	38	40	130	136
Operating Segments | Electric | Ameren Illinois Electric Distribution | Other
Disaggregation of Revenue [Line Items]
Revenues	(9)	(1)	(22)	(45)
Operating Segments | Electric | Ameren Illinois Natural Gas
Disaggregation of Revenue [Line Items]
Revenues	0	0	0	0
Operating Segments | Electric | Ameren Illinois Natural Gas | Residential
Disaggregation of Revenue [Line Items]
Operating Revenues	0	0	0	0
Operating Segments | Electric | Ameren Illinois Natural Gas | Commercial
Disaggregation of Revenue [Line Items]
Operating Revenues	0	0	0	0
Operating Segments | Electric | Ameren Illinois Natural Gas | Industrial
Disaggregation of Revenue [Line Items]
Operating Revenues	0	0	0	0
Operating Segments | Electric | Ameren Illinois Natural Gas | Other
Disaggregation of Revenue [Line Items]
Revenues	0	0	0	0
Operating Segments | Electric | Ameren Transmission
Disaggregation of Revenue [Line Items]
Revenues	210	188	586	512
Operating Segments | Electric | Ameren Transmission | Residential
Disaggregation of Revenue [Line Items]
Operating Revenues	0	0	0	0
Operating Segments | Electric | Ameren Transmission | Commercial
Disaggregation of Revenue [Line Items]
Operating Revenues	0	0	0	0
Operating Segments | Electric | Ameren Transmission | Industrial
Disaggregation of Revenue [Line Items]
Operating Revenues	0	0	0	0
Operating Segments | Electric | Ameren Transmission | Other
Disaggregation of Revenue [Line Items]
Revenues	210	188	586	512
Operating Segments | Natural gas | Union Electric Company
Disaggregation of Revenue [Line Items]
Revenues	18	18	103	123
Operating Segments | Natural gas | Union Electric Company | Residential
Disaggregation of Revenue [Line Items]
Operating Revenues	9	9	62	74
Operating Segments | Natural gas | Union Electric Company | Commercial
Disaggregation of Revenue [Line Items]
Operating Revenues	5	5	26	34
Operating Segments | Natural gas | Union Electric Company | Industrial
Disaggregation of Revenue [Line Items]
Operating Revenues	0	1	3	4
Operating Segments | Natural gas | Union Electric Company | Other
Disaggregation of Revenue [Line Items]
Revenues	4	3	12	11
Operating Segments | Natural gas | Ameren Illinois Electric Distribution
Disaggregation of Revenue [Line Items]
Revenues	0	0	0	0
Operating Segments | Natural gas | Ameren Illinois Electric Distribution | Residential
Disaggregation of Revenue [Line Items]
Operating Revenues	0	0	0	0
Operating Segments | Natural gas | Ameren Illinois Electric Distribution | Commercial
Disaggregation of Revenue [Line Items]
Operating Revenues	0	0	0	0
Operating Segments | Natural gas | Ameren Illinois Electric Distribution | Industrial
Disaggregation of Revenue [Line Items]
Operating Revenues	0	0	0	0
Operating Segments | Natural gas | Ameren Illinois Electric Distribution | Other
Disaggregation of Revenue [Line Items]
Revenues	0	0	0	0
Operating Segments | Natural gas | Ameren Illinois Natural Gas
Disaggregation of Revenue [Line Items]
Revenues	121	122	660	665
Operating Segments | Natural gas | Ameren Illinois Natural Gas | Residential
Disaggregation of Revenue [Line Items]
Operating Revenues	77	75	466	469
Operating Segments | Natural gas | Ameren Illinois Natural Gas | Commercial
Disaggregation of Revenue [Line Items]
Operating Revenues	19	19	111	121
Operating Segments | Natural gas | Ameren Illinois Natural Gas | Industrial
Disaggregation of Revenue [Line Items]
Operating Revenues	2	1	7	10
Operating Segments | Natural gas | Ameren Illinois Natural Gas | Other
Disaggregation of Revenue [Line Items]
Revenues	23	27	76	65
Operating Segments | Natural gas | Ameren Transmission
Disaggregation of Revenue [Line Items]
Revenues	0	0	0	0
Operating Segments | Natural gas | Ameren Transmission | Residential
Disaggregation of Revenue [Line Items]
Operating Revenues	0	0	0	0
Operating Segments | Natural gas | Ameren Transmission | Commercial
Disaggregation of Revenue [Line Items]
Operating Revenues	0	0	0	0
Operating Segments | Natural gas | Ameren Transmission | Industrial
Disaggregation of Revenue [Line Items]
Operating Revenues	0	0	0	0
Operating Segments | Natural gas | Ameren Transmission | Other
Disaggregation of Revenue [Line Items]
Revenues	0	0	0	0
Operating Segments | Ameren Illinois Company | Ameren Illinois Electric Distribution
Disaggregation of Revenue [Line Items]
Operating Revenues	552	558	1,567	1,722
Operating Segments | Ameren Illinois Company | Ameren Illinois Natural Gas
Disaggregation of Revenue [Line Items]
Operating Revenues	121	122	660	665
Operating Segments | Ameren Illinois Company | Ameren Illinois Transmission
Disaggregation of Revenue [Line Items]
Operating Revenues	120	103	332	276
Operating Segments | Ameren Illinois Company | Electric | Ameren Illinois Electric Distribution
Disaggregation of Revenue [Line Items]
Revenues	552	558	1,567	1,722
Operating Segments | Ameren Illinois Company | Electric | Ameren Illinois Electric Distribution | Residential
Disaggregation of Revenue [Line Items]
Operating Revenues	339	330	947	1,049
Operating Segments | Ameren Illinois Company | Electric | Ameren Illinois Electric Distribution | Commercial
Disaggregation of Revenue [Line Items]
Operating Revenues	184	189	512	582
Operating Segments | Ameren Illinois Company | Electric | Ameren Illinois Electric Distribution | Industrial
Disaggregation of Revenue [Line Items]
Operating Revenues	38	40	130	136
Operating Segments | Ameren Illinois Company | Electric | Ameren Illinois Electric Distribution | Other
Disaggregation of Revenue [Line Items]
Revenues	(9)	(1)	(22)	(45)
Operating Segments | Ameren Illinois Company | Electric | Ameren Illinois Transmission
Disaggregation of Revenue [Line Items]
Revenues	155	136	422	363
Operating Segments | Ameren Illinois Company | Electric | Ameren Illinois Transmission | Residential
Disaggregation of Revenue [Line Items]
Operating Revenues	0	0	0	0
Operating Segments | Ameren Illinois Company | Electric | Ameren Illinois Transmission | Commercial
Disaggregation of Revenue [Line Items]
Operating Revenues	0	0	0	0
Operating Segments | Ameren Illinois Company | Electric | Ameren Illinois Transmission | Industrial
Disaggregation of Revenue [Line Items]
Operating Revenues	0	0	0	0
Operating Segments | Ameren Illinois Company | Electric | Ameren Illinois Transmission | Other
Disaggregation of Revenue [Line Items]
Revenues	155	136	422	363
Operating Segments | Ameren Illinois Company | Natural gas | Ameren Illinois Natural Gas
Disaggregation of Revenue [Line Items]
Revenues	121	122	660	665
Operating Segments | Ameren Illinois Company | Natural gas | Ameren Illinois Natural Gas | Residential
Disaggregation of Revenue [Line Items]
Operating Revenues	77	75	466	469
Operating Segments | Ameren Illinois Company | Natural gas | Ameren Illinois Natural Gas | Commercial
Disaggregation of Revenue [Line Items]
Operating Revenues	19	19	111	121
Operating Segments | Ameren Illinois Company | Natural gas | Ameren Illinois Natural Gas | Industrial
Disaggregation of Revenue [Line Items]
Operating Revenues	2	1	7	10
Operating Segments | Ameren Illinois Company | Natural gas | Ameren Illinois Natural Gas | Other
Disaggregation of Revenue [Line Items]
Revenues	23	27	76	65
Intersegment Eliminations
Disaggregation of Revenue [Line Items]
Revenues	(52)	(45)	(136)	(118)
Revenues	(52)	(45)	(136)	(118)
Intersegment Eliminations | Union Electric Company
Disaggregation of Revenue [Line Items]
Revenues	(9)	(9)	(25)	(27)
Intersegment Eliminations | Ameren Illinois Electric Distribution
Disaggregation of Revenue [Line Items]
Revenues	(1)	(1)	(1)	(1)
Intersegment Eliminations | Ameren Illinois Natural Gas
Disaggregation of Revenue [Line Items]
Revenues	0	(1)	0	(1)
Intersegment Eliminations | Ameren Transmission
Disaggregation of Revenue [Line Items]
Revenues	(42)	(34)	(110)	(89)
Intersegment Eliminations | Electric
Disaggregation of Revenue [Line Items]
Revenues	(51)	(44)	(135)	(116)
Intersegment Eliminations | Electric | Residential
Disaggregation of Revenue [Line Items]
Operating Revenues	0	0	0	0
Intersegment Eliminations | Electric | Commercial
Disaggregation of Revenue [Line Items]
Operating Revenues	0	0	0	0
Intersegment Eliminations | Electric | Industrial
Disaggregation of Revenue [Line Items]
Operating Revenues	0	0	0	0
Intersegment Eliminations | Electric | Other
Disaggregation of Revenue [Line Items]
Revenues	(51)	(44)	(135)	(116)
Intersegment Eliminations | Natural gas
Disaggregation of Revenue [Line Items]
Revenues	(1)	(1)	(1)	(2)
Intersegment Eliminations | Natural gas | Residential
Disaggregation of Revenue [Line Items]
Operating Revenues	0	0	0	0
Intersegment Eliminations | Natural gas | Commercial
Disaggregation of Revenue [Line Items]
Operating Revenues	0	0	0	0
Intersegment Eliminations | Natural gas | Industrial
Disaggregation of Revenue [Line Items]
Operating Revenues	0	0	0	0
Intersegment Eliminations | Natural gas | Other
Disaggregation of Revenue [Line Items]
Revenues	(1)	(1)	(1)	(2)
Intersegment Eliminations | Ameren Illinois Company
Disaggregation of Revenue [Line Items]
Revenues	(35)	(33)	(90)	(87)
Revenues	(35)	(33)	(90)	(87)
Intersegment Eliminations | Ameren Illinois Company | Residential
Disaggregation of Revenue [Line Items]
Operating Revenues	0	0	0	0
Intersegment Eliminations | Ameren Illinois Company | Commercial
Disaggregation of Revenue [Line Items]
Operating Revenues	0	0	0	0
Intersegment Eliminations | Ameren Illinois Company | Industrial
Disaggregation of Revenue [Line Items]
Operating Revenues	0	0	0	0
Intersegment Eliminations | Ameren Illinois Company | Other
Disaggregation of Revenue [Line Items]
Revenues	(35)	(33)	(90)	(87)
Intersegment Eliminations | Ameren Illinois Company | Ameren Illinois Electric Distribution
Disaggregation of Revenue [Line Items]
Revenues	0	0	0	0
Intersegment Eliminations | Ameren Illinois Company | Ameren Illinois Natural Gas
Disaggregation of Revenue [Line Items]
Revenues	0	0	0	0
Intersegment Eliminations | Ameren Illinois Company | Ameren Illinois Transmission
Disaggregation of Revenue [Line Items]
Revenues	$ (35)	$ (33)	$ (90)	$ (87)