Segment Information (Disaggregation of Revenue) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2023	Jun. 30, 2022	Jun. 30, 2023	Jun. 30, 2022
Disaggregation of Revenue [Line Items]
Operating Revenues	$ 1,760	$ 1,726	$ 3,822	$ 3,605
Revenues	1,760	1,726	3,822	3,605
Revenues from alternative revenue programs	74	40	172	85
Other revenues not from contracts with customers	1	(34)	(2)	(31)
Union Electric Company
Disaggregation of Revenue [Line Items]
Revenues from alternative revenue programs	0	0	(2)	(6)
Other revenues not from contracts with customers	(2)	(36)	(8)	(36)
Ameren Illinois Electric Distribution
Disaggregation of Revenue [Line Items]
Revenues from alternative revenue programs	60	41	124	96
Other revenues not from contracts with customers	2	1	4	3
Ameren Illinois Natural Gas
Disaggregation of Revenue [Line Items]
Revenues from alternative revenue programs	9	3	37	(2)
Other revenues not from contracts with customers	1	1	2	2
Ameren Transmission
Disaggregation of Revenue [Line Items]
Revenues from alternative revenue programs	5	(4)	13	(3)
Other revenues not from contracts with customers	0	0	0	0
Electric
Disaggregation of Revenue [Line Items]
Operating Revenues	1,585	1,513	3,175	2,831
Revenues	1,585	1,513	3,175	2,831
Electric | Residential
Disaggregation of Revenue [Line Items]
Operating Revenues	697	655	1,403	1,250
Electric | Commercial
Disaggregation of Revenue [Line Items]
Operating Revenues	504	478	951	876
Electric | Industrial
Disaggregation of Revenue [Line Items]
Operating Revenues	123	126	232	228
Electric | Other
Disaggregation of Revenue [Line Items]
Revenues	261	254	589	477
Natural gas
Disaggregation of Revenue [Line Items]
Operating Revenues	175	213	647	774
Revenues	175	213	647	774
Natural gas | Residential
Disaggregation of Revenue [Line Items]
Operating Revenues	111	133	459	553
Natural gas | Commercial
Disaggregation of Revenue [Line Items]
Operating Revenues	31	38	131	157
Natural gas | Industrial
Disaggregation of Revenue [Line Items]
Operating Revenues	3	12	12	31
Natural gas | Other
Disaggregation of Revenue [Line Items]
Revenues	30	30	45	33
Ameren Illinois Company
Disaggregation of Revenue [Line Items]
Operating Revenues	779	769	1,880	1,793
Revenues	779	769	1,880	1,793
Revenues from alternative revenue programs	72	41	171	92
Other revenues not from contracts with customers	3	2	6	5
Ameren Illinois Company | Residential
Disaggregation of Revenue [Line Items]
Operating Revenues	435	401	1,113	1,033
Ameren Illinois Company | Commercial
Disaggregation of Revenue [Line Items]
Operating Revenues	218	210	495	465
Ameren Illinois Company | Industrial
Disaggregation of Revenue [Line Items]
Operating Revenues	50	64	105	126
Ameren Illinois Company | Other
Disaggregation of Revenue [Line Items]
Revenues	76	94	167	169
Ameren Illinois Company | Ameren Illinois Electric Distribution
Disaggregation of Revenue [Line Items]
Revenues from alternative revenue programs	60	41	124	96
Other revenues not from contracts with customers	2	1	4	3
Ameren Illinois Company | Ameren Illinois Natural Gas
Disaggregation of Revenue [Line Items]
Revenues from alternative revenue programs	9	3	37	(2)
Other revenues not from contracts with customers	1	1	2	2
Ameren Illinois Company | Ameren Illinois Transmission
Disaggregation of Revenue [Line Items]
Revenues from alternative revenue programs	3	(3)	10	(2)
Other revenues not from contracts with customers	0	0	0	0
Ameren Illinois Company | Electric
Disaggregation of Revenue [Line Items]
Operating Revenues	627	585	1,337	1,128
Ameren Illinois Company | Natural gas
Disaggregation of Revenue [Line Items]
Operating Revenues	152	184	543	665
Operating Segments | Union Electric Company
Disaggregation of Revenue [Line Items]
Operating Revenues	933	912	1,846	1,720
Revenues	941	919	1,864	1,737
Operating Segments | Ameren Illinois Electric Distribution
Disaggregation of Revenue [Line Items]
Operating Revenues	540	504	1,164	968
Revenues	540	504	1,164	969
Operating Segments | Ameren Illinois Natural Gas
Disaggregation of Revenue [Line Items]
Operating Revenues	152	184	543	665
Revenues	152	184	543	665
Operating Segments | Ameren Transmission
Disaggregation of Revenue [Line Items]
Operating Revenues	135	126	269	252
Revenues	161	150	324	296
Operating Segments | Electric | Union Electric Company
Disaggregation of Revenue [Line Items]
Revenues	918	890	1,759	1,628
Operating Segments | Electric | Union Electric Company | Residential
Disaggregation of Revenue [Line Items]
Operating Revenues	360	371	684	703
Operating Segments | Electric | Union Electric Company | Commercial
Disaggregation of Revenue [Line Items]
Operating Revenues	311	298	558	538
Operating Segments | Electric | Union Electric Company | Industrial
Disaggregation of Revenue [Line Items]
Operating Revenues	75	73	136	130
Operating Segments | Electric | Union Electric Company | Other
Disaggregation of Revenue [Line Items]
Revenues	172	148	381	257
Operating Segments | Electric | Ameren Illinois Electric Distribution
Disaggregation of Revenue [Line Items]
Revenues	540	504	1,164	969
Operating Segments | Electric | Ameren Illinois Electric Distribution | Residential
Disaggregation of Revenue [Line Items]
Operating Revenues	337	284	719	547
Operating Segments | Electric | Ameren Illinois Electric Distribution | Commercial
Disaggregation of Revenue [Line Items]
Operating Revenues	193	180	393	338
Operating Segments | Electric | Ameren Illinois Electric Distribution | Industrial
Disaggregation of Revenue [Line Items]
Operating Revenues	48	53	96	98
Operating Segments | Electric | Ameren Illinois Electric Distribution | Other
Disaggregation of Revenue [Line Items]
Revenues	(38)	(13)	(44)	(14)
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	161	150	324	296
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	161	150	324	296
Operating Segments | Natural gas | Union Electric Company
Disaggregation of Revenue [Line Items]
Revenues	23	29	105	109
Operating Segments | Natural gas | Union Electric Company | Residential
Disaggregation of Revenue [Line Items]
Operating Revenues	13	16	65	67
Operating Segments | Natural gas | Union Electric Company | Commercial
Disaggregation of Revenue [Line Items]
Operating Revenues	6	8	29	30
Operating Segments | Natural gas | Union Electric Company | Industrial
Disaggregation of Revenue [Line Items]
Operating Revenues	1	1	3	3
Operating Segments | Natural gas | Union Electric Company | Other
Disaggregation of Revenue [Line Items]
Revenues	3	4	8	9
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	152	184	543	665
Operating Segments | Natural gas | Ameren Illinois Natural Gas | Residential
Disaggregation of Revenue [Line Items]
Operating Revenues	98	117	394	486
Operating Segments | Natural gas | Ameren Illinois Natural Gas | Commercial
Disaggregation of Revenue [Line Items]
Operating Revenues	25	30	102	127
Operating Segments | Natural gas | Ameren Illinois Natural Gas | Industrial
Disaggregation of Revenue [Line Items]
Operating Revenues	2	11	9	28
Operating Segments | Natural gas | Ameren Illinois Natural Gas | Other
Disaggregation of Revenue [Line Items]
Revenues	27	26	38	24
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	540	504	1,164	969
Operating Segments | Ameren Illinois Company | Ameren Illinois Natural Gas
Disaggregation of Revenue [Line Items]
Operating Revenues	152	184	543	665
Operating Segments | Ameren Illinois Company | Ameren Illinois Transmission
Disaggregation of Revenue [Line Items]
Operating Revenues	87	81	173	159
Operating Segments | Ameren Illinois Company | Electric | Ameren Illinois Electric Distribution
Disaggregation of Revenue [Line Items]
Revenues	540	504	1,164	969
Operating Segments | Ameren Illinois Company | Electric | Ameren Illinois Electric Distribution | Residential
Disaggregation of Revenue [Line Items]
Operating Revenues	337	284	719	547
Operating Segments | Ameren Illinois Company | Electric | Ameren Illinois Electric Distribution | Commercial
Disaggregation of Revenue [Line Items]
Operating Revenues	193	180	393	338
Operating Segments | Ameren Illinois Company | Electric | Ameren Illinois Electric Distribution | Industrial
Disaggregation of Revenue [Line Items]
Operating Revenues	48	53	96	98
Operating Segments | Ameren Illinois Company | Electric | Ameren Illinois Electric Distribution | Other
Disaggregation of Revenue [Line Items]
Revenues	(38)	(13)	(44)	(14)
Operating Segments | Ameren Illinois Company | Electric | Ameren Illinois Transmission
Disaggregation of Revenue [Line Items]
Revenues	113	105	227	203
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	113	105	227	203
Operating Segments | Ameren Illinois Company | Natural gas | Ameren Illinois Natural Gas
Disaggregation of Revenue [Line Items]
Revenues	152	184	543	665
Operating Segments | Ameren Illinois Company | Natural gas | Ameren Illinois Natural Gas | Residential
Disaggregation of Revenue [Line Items]
Operating Revenues	98	117	394	486
Operating Segments | Ameren Illinois Company | Natural gas | Ameren Illinois Natural Gas | Commercial
Disaggregation of Revenue [Line Items]
Operating Revenues	25	30	102	127
Operating Segments | Ameren Illinois Company | Natural gas | Ameren Illinois Natural Gas | Industrial
Disaggregation of Revenue [Line Items]
Operating Revenues	2	11	9	28
Operating Segments | Ameren Illinois Company | Natural gas | Ameren Illinois Natural Gas | Other
Disaggregation of Revenue [Line Items]
Revenues	27	26	38	24
Intersegment Eliminations
Disaggregation of Revenue [Line Items]
Revenues	(34)	(31)	(73)	(62)
Revenues	(34)	(31)	(73)	(62)
Intersegment Eliminations | Union Electric Company
Disaggregation of Revenue [Line Items]
Revenues	(8)	(7)	(18)	(17)
Intersegment Eliminations | Ameren Illinois Electric Distribution
Disaggregation of Revenue [Line Items]
Revenues	0	0	0	(1)
Intersegment Eliminations | Ameren Illinois Natural Gas
Disaggregation of Revenue [Line Items]
Revenues	0	0	0	0
Intersegment Eliminations | Ameren Transmission
Disaggregation of Revenue [Line Items]
Revenues	(26)	(24)	(55)	(44)
Intersegment Eliminations | Electric
Disaggregation of Revenue [Line Items]
Revenues	(34)	(31)	(72)	(62)
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	(34)	(31)	(72)	(62)
Intersegment Eliminations | Natural gas
Disaggregation of Revenue [Line Items]
Revenues	0	0	(1)	0
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	0	0	(1)	0
Intersegment Eliminations | Ameren Illinois Company
Disaggregation of Revenue [Line Items]
Revenues	(26)	(24)	(54)	(44)
Revenues	(26)	(24)	(54)	(44)
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	(26)	(24)	(54)	(44)
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	$ (26)	$ (24)	$ (54)	$ (44)