Segment Information (Disaggregation of Revenue) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2022	Sep. 30, 2021	Sep. 30, 2022	Sep. 30, 2021
Disaggregation of Revenue [Line Items]
Revenues	$ 2,306	$ 1,811	$ 5,911	$ 4,849
Revenues	2,306	1,811	5,911	4,849
Revenues from alternative revenue programs	(83)	(95)	2	(6)
Other revenues not from contracts with customers	(43)	13	(74)	82
Union Electric Company
Disaggregation of Revenue [Line Items]
Revenues from alternative revenue programs	14	6	8	(9)
Other revenues not from contracts with customers	(45)	7	(81)	71
Ameren Illinois Electric Distribution
Disaggregation of Revenue [Line Items]
Revenues from alternative revenue programs	(83)	(97)	13	(2)
Other revenues not from contracts with customers	2	6	5	9
Ameren Illinois Natural Gas
Disaggregation of Revenue [Line Items]
Revenues from alternative revenue programs	(3)	(5)	(5)	0
Other revenues not from contracts with customers	0	0	2	2
Ameren Transmission
Disaggregation of Revenue [Line Items]
Revenues from alternative revenue programs	(11)	1	(14)	5
Other revenues not from contracts with customers	0	0	0	0
Electric
Disaggregation of Revenue [Line Items]
Revenues	2,140	1,668	4,971	4,108
Revenues	2,140	1,668	4,971	4,108
Electric | Residential
Disaggregation of Revenue [Line Items]
Revenues	971	795	2,221	1,882
Electric | Commercial
Disaggregation of Revenue [Line Items]
Revenues	663	555	1,539	1,301
Electric | Industrial
Disaggregation of Revenue [Line Items]
Revenues	146	124	374	315
Electric | Other
Disaggregation of Revenue [Line Items]
Revenues	360	194	837	610
Natural gas
Disaggregation of Revenue [Line Items]
Revenues	166	143	940	741
Revenues	166	143	940	741
Natural gas | Residential
Disaggregation of Revenue [Line Items]
Revenues	100	84	653	492
Natural gas | Commercial
Disaggregation of Revenue [Line Items]
Revenues	31	27	188	139
Natural gas | Industrial
Disaggregation of Revenue [Line Items]
Revenues	6	3	37	22
Natural gas | Other
Disaggregation of Revenue [Line Items]
Revenues	29	29	62	88
Ameren Illinois Company
Disaggregation of Revenue [Line Items]
Revenues	904	645	2,697	2,097
Revenues	904	645	2,697	2,097
Revenues from alternative revenue programs	(96)	(99)	(4)	2
Other revenues not from contracts with customers	2	6	7	11
Ameren Illinois Company | Residential
Disaggregation of Revenue [Line Items]
Revenues	496	333	1,529	1,143
Ameren Illinois Company | Commercial
Disaggregation of Revenue [Line Items]
Revenues	258	166	723	518
Ameren Illinois Company | Industrial
Disaggregation of Revenue [Line Items]
Revenues	52	29	178	114
Ameren Illinois Company | Other
Disaggregation of Revenue [Line Items]
Revenues	98	117	267	322
Ameren Illinois Company | Ameren Illinois Electric Distribution
Disaggregation of Revenue [Line Items]
Revenues from alternative revenue programs	(83)	(97)	13	(2)
Other revenues not from contracts with customers	2	6	5	9
Ameren Illinois Company | Ameren Illinois Natural Gas
Disaggregation of Revenue [Line Items]
Revenues from alternative revenue programs	(3)	(5)	(5)	0
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	(10)	3	(12)	4
Other revenues not from contracts with customers	0	0	0	0
Ameren Illinois Company | Electric
Disaggregation of Revenue [Line Items]
Revenues	758	518	1,886	1,455
Ameren Illinois Company | Natural gas
Disaggregation of Revenue [Line Items]
Revenues	146	127	811	642
Operating Segments | Union Electric Company
Disaggregation of Revenue [Line Items]
Revenues	1,351	1,118	3,071	2,612
Revenues	1,359	1,129	3,096	2,642
Operating Segments | Ameren Illinois Electric Distribution
Disaggregation of Revenue [Line Items]
Revenues	672	425	1,640	1,222
Revenues	672	428	1,641	1,227
Operating Segments | Ameren Illinois Natural Gas
Disaggregation of Revenue [Line Items]
Revenues	146	127	811	642
Revenues	146	127	811	642
Operating Segments | Ameren Transmission
Disaggregation of Revenue [Line Items]
Revenues	137	141	389	373
Revenues	169	160	465	426
Operating Segments | Electric | Union Electric Company
Disaggregation of Revenue [Line Items]
Revenues	1,338	1,113	2,966	2,543
Operating Segments | Electric | Union Electric Company | Residential
Disaggregation of Revenue [Line Items]
Revenues	564	537	1,267	1,177
Operating Segments | Electric | Union Electric Company | Commercial
Disaggregation of Revenue [Line Items]
Revenues	430	412	968	899
Operating Segments | Electric | Union Electric Company | Industrial
Disaggregation of Revenue [Line Items]
Revenues	99	98	229	221
Operating Segments | Electric | Union Electric Company | Other
Disaggregation of Revenue [Line Items]
Revenues	245	66	502	246
Operating Segments | Electric | Ameren Illinois Electric Distribution
Disaggregation of Revenue [Line Items]
Revenues	672	428	1,641	1,227
Operating Segments | Electric | Ameren Illinois Electric Distribution | Residential
Disaggregation of Revenue [Line Items]
Revenues	407	258	954	705
Operating Segments | Electric | Ameren Illinois Electric Distribution | Commercial
Disaggregation of Revenue [Line Items]
Revenues	233	143	571	402
Operating Segments | Electric | Ameren Illinois Electric Distribution | Industrial
Disaggregation of Revenue [Line Items]
Revenues	47	26	145	94
Operating Segments | Electric | Ameren Illinois Electric Distribution | Other
Disaggregation of Revenue [Line Items]
Revenues	(15)	1	(29)	26
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]
Revenues	0	0	0	0
Operating Segments | Electric | Ameren Illinois Natural Gas | Commercial
Disaggregation of Revenue [Line Items]
Revenues	0	0	0	0
Operating Segments | Electric | Ameren Illinois Natural Gas | Industrial
Disaggregation of Revenue [Line Items]
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	169	160	465	426
Operating Segments | Electric | Ameren Transmission | Residential
Disaggregation of Revenue [Line Items]
Revenues	0	0	0	0
Operating Segments | Electric | Ameren Transmission | Commercial
Disaggregation of Revenue [Line Items]
Revenues	0	0	0	0
Operating Segments | Electric | Ameren Transmission | Industrial
Disaggregation of Revenue [Line Items]
Revenues	0	0	0	0
Operating Segments | Electric | Ameren Transmission | Other
Disaggregation of Revenue [Line Items]
Revenues	169	160	465	426
Operating Segments | Natural gas | Union Electric Company
Disaggregation of Revenue [Line Items]
Revenues	21	16	130	99
Operating Segments | Natural gas | Union Electric Company | Residential
Disaggregation of Revenue [Line Items]
Revenues	11	9	78	54
Operating Segments | Natural gas | Union Electric Company | Commercial
Disaggregation of Revenue [Line Items]
Revenues	6	4	36	23
Operating Segments | Natural gas | Union Electric Company | Industrial
Disaggregation of Revenue [Line Items]
Revenues	1	0	4	2
Operating Segments | Natural gas | Union Electric Company | Other
Disaggregation of Revenue [Line Items]
Revenues	3	3	12	20
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]
Revenues	0	0	0	0
Operating Segments | Natural gas | Ameren Illinois Electric Distribution | Commercial
Disaggregation of Revenue [Line Items]
Revenues	0	0	0	0
Operating Segments | Natural gas | Ameren Illinois Electric Distribution | Industrial
Disaggregation of Revenue [Line Items]
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	146	127	811	642
Operating Segments | Natural gas | Ameren Illinois Natural Gas | Residential
Disaggregation of Revenue [Line Items]
Revenues	89	75	575	438
Operating Segments | Natural gas | Ameren Illinois Natural Gas | Commercial
Disaggregation of Revenue [Line Items]
Revenues	25	23	152	116
Operating Segments | Natural gas | Ameren Illinois Natural Gas | Industrial
Disaggregation of Revenue [Line Items]
Revenues	5	3	33	20
Operating Segments | Natural gas | Ameren Illinois Natural Gas | Other
Disaggregation of Revenue [Line Items]
Revenues	27	26	51	68
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]
Revenues	0	0	0	0
Operating Segments | Natural gas | Ameren Transmission | Commercial
Disaggregation of Revenue [Line Items]
Revenues	0	0	0	0
Operating Segments | Natural gas | Ameren Transmission | Industrial
Disaggregation of Revenue [Line Items]
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]
Revenues	672	428	1,641	1,227
Operating Segments | Ameren Illinois Company | Ameren Illinois Natural Gas
Disaggregation of Revenue [Line Items]
Revenues	146	127	811	642
Operating Segments | Ameren Illinois Company | Ameren Illinois Transmission
Disaggregation of Revenue [Line Items]
Revenues	86	90	245	228
Operating Segments | Ameren Illinois Company | Electric | Ameren Illinois Electric Distribution
Disaggregation of Revenue [Line Items]
Revenues	672	428	1,641	1,227
Operating Segments | Ameren Illinois Company | Electric | Ameren Illinois Electric Distribution | Residential
Disaggregation of Revenue [Line Items]
Revenues	407	258	954	705
Operating Segments | Ameren Illinois Company | Electric | Ameren Illinois Electric Distribution | Commercial
Disaggregation of Revenue [Line Items]
Revenues	233	143	571	402
Operating Segments | Ameren Illinois Company | Electric | Ameren Illinois Electric Distribution | Industrial
Disaggregation of Revenue [Line Items]
Revenues	47	26	145	94
Operating Segments | Ameren Illinois Company | Electric | Ameren Illinois Electric Distribution | Other
Disaggregation of Revenue [Line Items]
Revenues	(15)	1	(29)	26
Operating Segments | Ameren Illinois Company | Electric | Ameren Illinois Transmission
Disaggregation of Revenue [Line Items]
Revenues	117	108	320	277
Operating Segments | Ameren Illinois Company | Electric | Ameren Illinois Transmission | Residential
Disaggregation of Revenue [Line Items]
Revenues	0	0	0	0
Operating Segments | Ameren Illinois Company | Electric | Ameren Illinois Transmission | Commercial
Disaggregation of Revenue [Line Items]
Revenues	0	0	0	0
Operating Segments | Ameren Illinois Company | Electric | Ameren Illinois Transmission | Industrial
Disaggregation of Revenue [Line Items]
Revenues	0	0	0	0
Operating Segments | Ameren Illinois Company | Electric | Ameren Illinois Transmission | Other
Disaggregation of Revenue [Line Items]
Revenues	117	108	320	277
Operating Segments | Ameren Illinois Company | Natural gas | Ameren Illinois Natural Gas
Disaggregation of Revenue [Line Items]
Revenues	146	127	811	642
Operating Segments | Ameren Illinois Company | Natural gas | Ameren Illinois Natural Gas | Residential
Disaggregation of Revenue [Line Items]
Revenues	89	75	575	438
Operating Segments | Ameren Illinois Company | Natural gas | Ameren Illinois Natural Gas | Commercial
Disaggregation of Revenue [Line Items]
Revenues	25	23	152	116
Operating Segments | Ameren Illinois Company | Natural gas | Ameren Illinois Natural Gas | Industrial
Disaggregation of Revenue [Line Items]
Revenues	5	3	33	20
Operating Segments | Ameren Illinois Company | Natural gas | Ameren Illinois Natural Gas | Other
Disaggregation of Revenue [Line Items]
Revenues	27	26	51	68
Intersegment Eliminations
Disaggregation of Revenue [Line Items]
Revenues	(40)	(33)	(102)	(88)
Revenues	(40)	(33)	(102)	(88)
Intersegment Eliminations | Union Electric Company
Disaggregation of Revenue [Line Items]
Revenues	(8)	(11)	(25)	(30)
Intersegment Eliminations | Ameren Illinois Electric Distribution
Disaggregation of Revenue [Line Items]
Revenues	0	(3)	(1)	(5)
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	(32)	(19)	(76)	(53)
Intersegment Eliminations | Electric
Disaggregation of Revenue [Line Items]
Revenues	(39)	(33)	(101)	(88)
Intersegment Eliminations | Electric | Residential
Disaggregation of Revenue [Line Items]
Revenues	0	0	0	0
Intersegment Eliminations | Electric | Commercial
Disaggregation of Revenue [Line Items]
Revenues	0	0	0	0
Intersegment Eliminations | Electric | Industrial
Disaggregation of Revenue [Line Items]
Revenues	0	0	0	0
Intersegment Eliminations | Electric | Other
Disaggregation of Revenue [Line Items]
Revenues	(39)	(33)	(101)	(88)
Intersegment Eliminations | Natural gas
Disaggregation of Revenue [Line Items]
Revenues	(1)	0	(1)	0
Intersegment Eliminations | Natural gas | Residential
Disaggregation of Revenue [Line Items]
Revenues	0	0	0	0
Intersegment Eliminations | Natural gas | Commercial
Disaggregation of Revenue [Line Items]
Revenues	0	0	0	0
Intersegment Eliminations | Natural gas | Industrial
Disaggregation of Revenue [Line Items]
Revenues	0	0	0	0
Intersegment Eliminations | Natural gas | Other
Disaggregation of Revenue [Line Items]
Revenues	(1)	0	(1)	0
Intersegment Eliminations | Ameren Illinois Company
Disaggregation of Revenue [Line Items]
Revenues	(31)	(18)	(75)	(49)
Revenues	(31)	(18)	(75)	(49)
Intersegment Eliminations | Ameren Illinois Company | Residential
Disaggregation of Revenue [Line Items]
Revenues	0	0	0	0
Intersegment Eliminations | Ameren Illinois Company | Commercial
Disaggregation of Revenue [Line Items]
Revenues	0	0	0	0
Intersegment Eliminations | Ameren Illinois Company | Industrial
Disaggregation of Revenue [Line Items]
Revenues	0	0	0	0
Intersegment Eliminations | Ameren Illinois Company | Other
Disaggregation of Revenue [Line Items]
Revenues	(31)	(18)	(75)	(49)
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	$ (31)	$ (18)	$ (75)	$ (49)