Segment Information (Disaggregation of Revenue) (Details) - USD ($) $ in Millions	3 Months Ended
Mar. 31, 2025	Mar. 31, 2024
Disaggregation of Revenue [Line Items]
Operating Revenues	$ 2,097	$ 1,816
Revenues	2,097	1,816
Revenues from alternative revenue programs	18	61
Other revenues not from contracts with customers	5	4
Union Electric Company
Disaggregation of Revenue [Line Items]
Revenues from alternative revenue programs	(5)	(6)
Other revenues not from contracts with customers	1	1
Ameren Illinois Electric Distribution
Disaggregation of Revenue [Line Items]
Revenues from alternative revenue programs	21	39
Other revenues not from contracts with customers	3	2
Ameren Illinois Natural Gas
Disaggregation of Revenue [Line Items]
Revenues from alternative revenue programs	3	19
Other revenues not from contracts with customers	1	1
Ameren Transmission
Disaggregation of Revenue [Line Items]
Revenues from alternative revenue programs	(1)	9
Other revenues not from contracts with customers	0	0
Electric
Disaggregation of Revenue [Line Items]
Operating Revenues	1,622	1,364
Revenues	1,622	1,364
Electric \| Residential
Disaggregation of Revenue [Line Items]
Operating Revenues	718	638
Electric \| Commercial
Disaggregation of Revenue [Line Items]
Operating Revenues	453	424
Electric \| Industrial
Disaggregation of Revenue [Line Items]
Operating Revenues	116	106
Electric \| Other
Disaggregation of Revenue [Line Items]
Revenues	335	196
Natural gas
Disaggregation of Revenue [Line Items]
Operating Revenues	475	452
Revenues	475	452
Natural gas \| Residential
Disaggregation of Revenue [Line Items]
Operating Revenues	352	327
Natural gas \| Commercial
Disaggregation of Revenue [Line Items]
Operating Revenues	96	84
Natural gas \| Industrial
Disaggregation of Revenue [Line Items]
Operating Revenues	6	6
Natural gas \| Other
Disaggregation of Revenue [Line Items]
Revenues	21	35
Ameren Illinois Company
Disaggregation of Revenue [Line Items]
Operating Revenues	1,100	1,000
Revenues	1,100	1,000
Revenues from alternative revenue programs	23	66
Other revenues not from contracts with customers	4	3
Ameren Illinois Company \| Residential
Disaggregation of Revenue [Line Items]
Operating Revenues	651	584
Ameren Illinois Company \| Commercial
Disaggregation of Revenue [Line Items]
Operating Revenues	257	233
Ameren Illinois Company \| Industrial
Disaggregation of Revenue [Line Items]
Operating Revenues	54	49
Ameren Illinois Company \| Other
Disaggregation of Revenue [Line Items]
Revenues	138	134
Ameren Illinois Company \| Ameren Illinois Electric Distribution
Disaggregation of Revenue [Line Items]
Revenues from alternative revenue programs	21	39
Other revenues not from contracts with customers	3	2
Ameren Illinois Company \| Ameren Illinois Natural Gas
Disaggregation of Revenue [Line Items]
Revenues from alternative revenue programs	3	19
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	(1)	8
Other revenues not from contracts with customers	0	0
Ameren Illinois Company \| Electric
Disaggregation of Revenue [Line Items]
Operating Revenues	689	609
Ameren Illinois Company \| Natural gas
Disaggregation of Revenue [Line Items]
Operating Revenues	411	391
Operating Segments \| Union Electric Company
Disaggregation of Revenue [Line Items]
Operating Revenues	950	768
Revenues	957	775
Operating Segments \| Ameren Illinois Electric Distribution
Disaggregation of Revenue [Line Items]
Operating Revenues	570	506
Revenues	572	506
Operating Segments \| Ameren Illinois Natural Gas
Disaggregation of Revenue [Line Items]
Operating Revenues	411	391
Revenues	411	391
Operating Segments \| Ameren Transmission
Disaggregation of Revenue [Line Items]
Operating Revenues	166	151
Revenues	210	185
Operating Segments \| Electric \| Union Electric Company
Disaggregation of Revenue [Line Items]
Revenues	893	714
Operating Segments \| Electric \| Union Electric Company \| Residential
Disaggregation of Revenue [Line Items]
Operating Revenues	376	341
Operating Segments \| Electric \| Union Electric Company \| Commercial
Disaggregation of Revenue [Line Items]
Operating Revenues	273	259
Operating Segments \| Electric \| Union Electric Company \| Industrial
Disaggregation of Revenue [Line Items]
Operating Revenues	66	61
Operating Segments \| Electric \| Union Electric Company \| Other
Disaggregation of Revenue [Line Items]
Revenues	178	53
Operating Segments \| Electric \| Ameren Illinois Electric Distribution
Disaggregation of Revenue [Line Items]
Revenues	572	506
Operating Segments \| Electric \| Ameren Illinois Electric Distribution \| Residential
Disaggregation of Revenue [Line Items]
Operating Revenues	342	297
Operating Segments \| Electric \| Ameren Illinois Electric Distribution \| Commercial
Disaggregation of Revenue [Line Items]
Operating Revenues	180	165
Operating Segments \| Electric \| Ameren Illinois Electric Distribution \| Industrial
Disaggregation of Revenue [Line Items]
Operating Revenues	50	45
Operating Segments \| Electric \| Ameren Illinois Electric Distribution \| Other
Disaggregation of Revenue [Line Items]
Revenues	0	(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]
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	210	185
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	210	185
Operating Segments \| Natural gas \| Union Electric Company
Disaggregation of Revenue [Line Items]
Revenues	64	61
Operating Segments \| Natural gas \| Union Electric Company \| Residential
Disaggregation of Revenue [Line Items]
Operating Revenues	43	40
Operating Segments \| Natural gas \| Union Electric Company \| Commercial
Disaggregation of Revenue [Line Items]
Operating Revenues	19	16
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	0	3
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	411	391
Operating Segments \| Natural gas \| Ameren Illinois Natural Gas \| Residential
Disaggregation of Revenue [Line Items]
Operating Revenues	309	287
Operating Segments \| Natural gas \| Ameren Illinois Natural Gas \| Commercial
Disaggregation of Revenue [Line Items]
Operating Revenues	77	68
Operating Segments \| Natural gas \| Ameren Illinois Natural Gas \| Industrial
Disaggregation of Revenue [Line Items]
Operating Revenues	4	4
Operating Segments \| Natural gas \| Ameren Illinois Natural Gas \| Other
Disaggregation of Revenue [Line Items]
Revenues	21	32
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	572	506
Revenues	572	506
Operating Segments \| Ameren Illinois Company \| Ameren Illinois Natural Gas
Disaggregation of Revenue [Line Items]
Operating Revenues	411	391
Revenues	411	391
Operating Segments \| Ameren Illinois Company \| Ameren Illinois Transmission
Disaggregation of Revenue [Line Items]
Operating Revenues	117	103
Revenues	154	131
Operating Segments \| Ameren Illinois Company \| Electric \| Ameren Illinois Electric Distribution
Disaggregation of Revenue [Line Items]
Revenues	572	506
Operating Segments \| Ameren Illinois Company \| Electric \| Ameren Illinois Electric Distribution \| Residential
Disaggregation of Revenue [Line Items]
Operating Revenues	342	297
Operating Segments \| Ameren Illinois Company \| Electric \| Ameren Illinois Electric Distribution \| Commercial
Disaggregation of Revenue [Line Items]
Operating Revenues	180	165
Operating Segments \| Ameren Illinois Company \| Electric \| Ameren Illinois Electric Distribution \| Industrial
Disaggregation of Revenue [Line Items]
Operating Revenues	50	45
Operating Segments \| Ameren Illinois Company \| Electric \| Ameren Illinois Electric Distribution \| Other
Disaggregation of Revenue [Line Items]
Revenues	0	(1)
Operating Segments \| Ameren Illinois Company \| Electric \| Ameren Illinois Transmission
Disaggregation of Revenue [Line Items]
Revenues	154	131
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	154	131
Operating Segments \| Ameren Illinois Company \| Natural gas \| Ameren Illinois Natural Gas
Disaggregation of Revenue [Line Items]
Revenues	411	391
Operating Segments \| Ameren Illinois Company \| Natural gas \| Ameren Illinois Natural Gas \| Residential
Disaggregation of Revenue [Line Items]
Operating Revenues	309	287
Operating Segments \| Ameren Illinois Company \| Natural gas \| Ameren Illinois Natural Gas \| Commercial
Disaggregation of Revenue [Line Items]
Operating Revenues	77	68
Operating Segments \| Ameren Illinois Company \| Natural gas \| Ameren Illinois Natural Gas \| Industrial
Disaggregation of Revenue [Line Items]
Operating Revenues	4	4
Operating Segments \| Ameren Illinois Company \| Natural gas \| Ameren Illinois Natural Gas \| Other
Disaggregation of Revenue [Line Items]
Revenues	21	32
Intersegment Eliminations
Disaggregation of Revenue [Line Items]
Revenues	(53)	(41)
Revenues	(53)	(41)
Intersegment Eliminations \| Union Electric Company
Disaggregation of Revenue [Line Items]
Revenues	(7)	(7)
Intersegment Eliminations \| Ameren Illinois Electric Distribution
Disaggregation of Revenue [Line Items]
Revenues	(2)	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	(44)	(34)
Intersegment Eliminations \| Electric
Disaggregation of Revenue [Line Items]
Revenues	(53)	(41)
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	(53)	(41)
Intersegment Eliminations \| Natural gas
Disaggregation of Revenue [Line Items]
Revenues	0	0
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	0
Intersegment Eliminations \| Ameren Illinois Company
Disaggregation of Revenue [Line Items]
Revenues	(37)	(28)
Revenues	(37)	(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	(37)	(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	$ (37)	$ (28)

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