Segment Information (Disaggregation of Revenue) (Details) - USD ($) $ in Millions	3 Months Ended
Mar. 31, 2024	Mar. 31, 2023
Disaggregation of Revenue [Line Items]
Operating Revenues	$ 1,816	$ 2,062
Revenues	1,816	2,062
Revenues from alternative revenue programs	61	98
Other revenues not from contracts with customers	4	(3)
Union Electric Company
Disaggregation of Revenue [Line Items]
Revenues from alternative revenue programs	(6)	(2)
Other revenues not from contracts with customers	1	(6)
Ameren Illinois Electric Distribution
Disaggregation of Revenue [Line Items]
Revenues from alternative revenue programs	39	64
Other revenues not from contracts with customers	2	2
Ameren Illinois Natural Gas
Disaggregation of Revenue [Line Items]
Revenues from alternative revenue programs	19	28
Other revenues not from contracts with customers	1	1
Ameren Transmission
Disaggregation of Revenue [Line Items]
Revenues from alternative revenue programs	9	8
Other revenues not from contracts with customers	0	0
Electric
Disaggregation of Revenue [Line Items]
Operating Revenues	1,364	1,590
Revenues	1,364	1,590
Electric \| Residential
Disaggregation of Revenue [Line Items]
Operating Revenues	638	706
Electric \| Commercial
Disaggregation of Revenue [Line Items]
Operating Revenues	424	447
Electric \| Industrial
Disaggregation of Revenue [Line Items]
Operating Revenues	106	109
Electric \| Other
Disaggregation of Revenue [Line Items]
Revenues	196	328
Natural gas
Disaggregation of Revenue [Line Items]
Operating Revenues	452	472
Revenues	452	472
Natural gas \| Residential
Disaggregation of Revenue [Line Items]
Operating Revenues	327	348
Natural gas \| Commercial
Disaggregation of Revenue [Line Items]
Operating Revenues	84	100
Natural gas \| Industrial
Disaggregation of Revenue [Line Items]
Operating Revenues	6	9
Natural gas \| Other
Disaggregation of Revenue [Line Items]
Revenues	35	15
Ameren Illinois Company
Disaggregation of Revenue [Line Items]
Operating Revenues	1,000	1,101
Revenues	1,000	1,101
Revenues from alternative revenue programs	66	99
Other revenues not from contracts with customers	3	3
Ameren Illinois Company \| Residential
Disaggregation of Revenue [Line Items]
Operating Revenues	584	678
Ameren Illinois Company \| Commercial
Disaggregation of Revenue [Line Items]
Operating Revenues	233	277
Ameren Illinois Company \| Industrial
Disaggregation of Revenue [Line Items]
Operating Revenues	49	55
Ameren Illinois Company \| Other
Disaggregation of Revenue [Line Items]
Revenues	134	91
Ameren Illinois Company \| Ameren Illinois Electric Distribution
Disaggregation of Revenue [Line Items]
Revenues from alternative revenue programs	39	64
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	19	28
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	8	7
Other revenues not from contracts with customers	0	0
Ameren Illinois Company \| Electric
Disaggregation of Revenue [Line Items]
Operating Revenues	609	710
Ameren Illinois Company \| Natural gas
Disaggregation of Revenue [Line Items]
Operating Revenues	391	391
Operating Segments \| Union Electric Company
Disaggregation of Revenue [Line Items]
Operating Revenues	768	913
Revenues	775	923
Operating Segments \| Ameren Illinois Electric Distribution
Disaggregation of Revenue [Line Items]
Operating Revenues	506	624
Revenues	506	624
Operating Segments \| Ameren Illinois Natural Gas
Disaggregation of Revenue [Line Items]
Operating Revenues	391	391
Revenues	391	391
Operating Segments \| Ameren Transmission
Disaggregation of Revenue [Line Items]
Operating Revenues	151	134
Revenues	185	163
Operating Segments \| Electric \| Union Electric Company
Disaggregation of Revenue [Line Items]
Revenues	714	841
Operating Segments \| Electric \| Union Electric Company \| Residential
Disaggregation of Revenue [Line Items]
Operating Revenues	341	324
Operating Segments \| Electric \| Union Electric Company \| Commercial
Disaggregation of Revenue [Line Items]
Operating Revenues	259	247
Operating Segments \| Electric \| Union Electric Company \| Industrial
Disaggregation of Revenue [Line Items]
Operating Revenues	61	61
Operating Segments \| Electric \| Union Electric Company \| Other
Disaggregation of Revenue [Line Items]
Revenues	53	209
Operating Segments \| Electric \| Ameren Illinois Electric Distribution
Disaggregation of Revenue [Line Items]
Revenues	506	624
Operating Segments \| Electric \| Ameren Illinois Electric Distribution \| Residential
Disaggregation of Revenue [Line Items]
Operating Revenues	297	382
Operating Segments \| Electric \| Ameren Illinois Electric Distribution \| Commercial
Disaggregation of Revenue [Line Items]
Operating Revenues	165	200
Operating Segments \| Electric \| Ameren Illinois Electric Distribution \| Industrial
Disaggregation of Revenue [Line Items]
Operating Revenues	45	48
Operating Segments \| Electric \| Ameren Illinois Electric Distribution \| Other
Disaggregation of Revenue [Line Items]
Revenues	(1)	(6)
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]
Operating Revenues	0	0
Operating Segments \| Electric \| Ameren Illinois Natural Gas \| Commercial
Disaggregation of Revenue [Line Items]
Operating Revenues	0	0
Operating Segments \| Electric \| Ameren Illinois Natural Gas \| Industrial
Disaggregation of Revenue [Line Items]
Operating 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	185	163
Operating Segments \| Electric \| Ameren Transmission \| Residential
Disaggregation of Revenue [Line Items]
Operating Revenues	0	0
Operating Segments \| Electric \| Ameren Transmission \| Commercial
Disaggregation of Revenue [Line Items]
Operating Revenues	0	0
Operating Segments \| Electric \| Ameren Transmission \| Industrial
Disaggregation of Revenue [Line Items]
Operating Revenues	0	0
Operating Segments \| Electric \| Ameren Transmission \| Other
Disaggregation of Revenue [Line Items]
Revenues	185	163
Operating Segments \| Natural gas \| Union Electric Company
Disaggregation of Revenue [Line Items]
Revenues	61	82
Operating Segments \| Natural gas \| Union Electric Company \| Residential
Disaggregation of Revenue [Line Items]
Operating Revenues	40	52
Operating Segments \| Natural gas \| Union Electric Company \| Commercial
Disaggregation of Revenue [Line Items]
Operating Revenues	16	23
Operating Segments \| Natural gas \| Union Electric Company \| Industrial
Disaggregation of Revenue [Line Items]
Operating Revenues	2	2
Operating Segments \| Natural gas \| Union Electric Company \| Other
Disaggregation of Revenue [Line Items]
Revenues	3	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]
Operating Revenues	0	0
Operating Segments \| Natural gas \| Ameren Illinois Electric Distribution \| Commercial
Disaggregation of Revenue [Line Items]
Operating Revenues	0	0
Operating Segments \| Natural gas \| Ameren Illinois Electric Distribution \| Industrial
Disaggregation of Revenue [Line Items]
Operating 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	391
Operating Segments \| Natural gas \| Ameren Illinois Natural Gas \| Residential
Disaggregation of Revenue [Line Items]
Operating Revenues	287	296
Operating Segments \| Natural gas \| Ameren Illinois Natural Gas \| Commercial
Disaggregation of Revenue [Line Items]
Operating Revenues	68	77
Operating Segments \| Natural gas \| Ameren Illinois Natural Gas \| Industrial
Disaggregation of Revenue [Line Items]
Operating Revenues	4	7
Operating Segments \| Natural gas \| Ameren Illinois Natural Gas \| Other
Disaggregation of Revenue [Line Items]
Revenues	32	11
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]
Operating Revenues	0	0
Operating Segments \| Natural gas \| Ameren Transmission \| Commercial
Disaggregation of Revenue [Line Items]
Operating Revenues	0	0
Operating Segments \| Natural gas \| Ameren Transmission \| Industrial
Disaggregation of Revenue [Line Items]
Operating 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]
Operating Revenues	506	624
Operating Segments \| Ameren Illinois Company \| Ameren Illinois Natural Gas
Disaggregation of Revenue [Line Items]
Operating Revenues	391	391
Operating Segments \| Ameren Illinois Company \| Ameren Illinois Transmission
Disaggregation of Revenue [Line Items]
Operating Revenues	103	86
Operating Segments \| Ameren Illinois Company \| Electric \| Ameren Illinois Electric Distribution
Disaggregation of Revenue [Line Items]
Revenues	506	624
Operating Segments \| Ameren Illinois Company \| Electric \| Ameren Illinois Electric Distribution \| Residential
Disaggregation of Revenue [Line Items]
Operating Revenues	297	382
Operating Segments \| Ameren Illinois Company \| Electric \| Ameren Illinois Electric Distribution \| Commercial
Disaggregation of Revenue [Line Items]
Operating Revenues	165	200
Operating Segments \| Ameren Illinois Company \| Electric \| Ameren Illinois Electric Distribution \| Industrial
Disaggregation of Revenue [Line Items]
Operating Revenues	45	48
Operating Segments \| Ameren Illinois Company \| Electric \| Ameren Illinois Electric Distribution \| Other
Disaggregation of Revenue [Line Items]
Revenues	(1)	(6)
Operating Segments \| Ameren Illinois Company \| Electric \| Ameren Illinois Transmission
Disaggregation of Revenue [Line Items]
Revenues	131	114
Operating Segments \| Ameren Illinois Company \| Electric \| Ameren Illinois Transmission \| Residential
Disaggregation of Revenue [Line Items]
Operating Revenues	0	0
Operating Segments \| Ameren Illinois Company \| Electric \| Ameren Illinois Transmission \| Commercial
Disaggregation of Revenue [Line Items]
Operating Revenues	0	0
Operating Segments \| Ameren Illinois Company \| Electric \| Ameren Illinois Transmission \| Industrial
Disaggregation of Revenue [Line Items]
Operating Revenues	0	0
Operating Segments \| Ameren Illinois Company \| Electric \| Ameren Illinois Transmission \| Other
Disaggregation of Revenue [Line Items]
Revenues	131	114
Operating Segments \| Ameren Illinois Company \| Natural gas \| Ameren Illinois Natural Gas
Disaggregation of Revenue [Line Items]
Revenues	391	391
Operating Segments \| Ameren Illinois Company \| Natural gas \| Ameren Illinois Natural Gas \| Residential
Disaggregation of Revenue [Line Items]
Operating Revenues	287	296
Operating Segments \| Ameren Illinois Company \| Natural gas \| Ameren Illinois Natural Gas \| Commercial
Disaggregation of Revenue [Line Items]
Operating Revenues	68	77
Operating Segments \| Ameren Illinois Company \| Natural gas \| Ameren Illinois Natural Gas \| Industrial
Disaggregation of Revenue [Line Items]
Operating Revenues	4	7
Operating Segments \| Ameren Illinois Company \| Natural gas \| Ameren Illinois Natural Gas \| Other
Disaggregation of Revenue [Line Items]
Revenues	32	11
Intersegment Eliminations
Disaggregation of Revenue [Line Items]
Revenues	(41)	(39)
Revenues	(41)	(39)
Intersegment Eliminations \| Union Electric Company
Disaggregation of Revenue [Line Items]
Revenues	(7)	(10)
Intersegment Eliminations \| Ameren Illinois Electric Distribution
Disaggregation of Revenue [Line Items]
Revenues	0	0
Intersegment Eliminations \| Ameren Illinois Natural Gas
Disaggregation of Revenue [Line Items]
Revenues	0	0
Intersegment Eliminations \| Ameren Transmission
Disaggregation of Revenue [Line Items]
Revenues	(34)	(29)
Intersegment Eliminations \| Electric
Disaggregation of Revenue [Line Items]
Revenues	(41)	(38)
Intersegment Eliminations \| Electric \| Residential
Disaggregation of Revenue [Line Items]
Operating Revenues	0	0
Intersegment Eliminations \| Electric \| Commercial
Disaggregation of Revenue [Line Items]
Operating Revenues	0	0
Intersegment Eliminations \| Electric \| Industrial
Disaggregation of Revenue [Line Items]
Operating Revenues	0	0
Intersegment Eliminations \| Electric \| Other
Disaggregation of Revenue [Line Items]
Revenues	(41)	(38)
Intersegment Eliminations \| Natural gas
Disaggregation of Revenue [Line Items]
Revenues	0	(1)
Intersegment Eliminations \| Natural gas \| Residential
Disaggregation of Revenue [Line Items]
Operating Revenues	0	0
Intersegment Eliminations \| Natural gas \| Commercial
Disaggregation of Revenue [Line Items]
Operating Revenues	0	0
Intersegment Eliminations \| Natural gas \| Industrial
Disaggregation of Revenue [Line Items]
Operating Revenues	0	0
Intersegment Eliminations \| Natural gas \| Other
Disaggregation of Revenue [Line Items]
Revenues	0	(1)
Intersegment Eliminations \| Ameren Illinois Company
Disaggregation of Revenue [Line Items]
Revenues	(28)	(28)
Revenues	(28)	(28)
Intersegment Eliminations \| Ameren Illinois Company \| Residential
Disaggregation of Revenue [Line Items]
Operating Revenues	0	0
Intersegment Eliminations \| Ameren Illinois Company \| Commercial
Disaggregation of Revenue [Line Items]
Operating Revenues	0	0
Intersegment Eliminations \| Ameren Illinois Company \| Industrial
Disaggregation of Revenue [Line Items]
Operating Revenues	0	0
Intersegment Eliminations \| Ameren Illinois Company \| Other
Disaggregation of Revenue [Line Items]
Revenues	(28)	(28)
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)	$ (28)

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