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Segment Information (Disaggregation of Revenue) (Details) - USD ($) $ in Millions | 3 Months Ended | 9 Months Ended
--- | --- | ---
Sep. 30, 2023 | Sep. 30, 2022 | Sep. 30, 2023 | Sep. 30, 2022
Disaggregation of Revenue [Line Items] |  |  |  |
Operating Revenues | $ 2,060 | $ 2,306 | $ 5,882 | $ 5,911
Revenues | 2,060 | 2,306 | 5,882 | 5,911
Revenues from alternative revenue programs | (109) | (83) | 63 | 2
Other revenues not from contracts with customers | 1 | (43) | (1) | (74)
Union Electric Company |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenues from alternative revenue programs | (9) | 14 | (11) | 8
Other revenues not from contracts with customers | (1) | (45) | (9) | (81)
Ameren Illinois Electric Distribution |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenues from alternative revenue programs | (94) | (83) | 30 | 13
Other revenues not from contracts with customers | 2 | 2 | 6 | 5
Ameren Illinois Natural Gas |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenues from alternative revenue programs | (1) | (3) | 36 | (5)
Other revenues not from contracts with customers | 0 | 0 | 2 | 2
Ameren Transmission |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenues from alternative revenue programs | (5) | (11) | 8 | (14)
Other revenues not from contracts with customers | 0 | 0 | 0 | 0
Electric |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Operating Revenues | 1,921 | 2,140 | 5,096 | 4,971
Revenues | 1,921 | 2,140 | 5,096 | 4,971
Electric | Residential |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Operating Revenues | 920 | 971 | 2,323 | 2,221
Electric | Commercial |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Operating Revenues | 657 | 663 | 1,608 | 1,539
Electric | Industrial |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Operating Revenues | 147 | 146 | 379 | 374
Electric | Other |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenues | 197 | 360 | 786 | 837
Natural gas |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Operating Revenues | 139 | 166 | 786 | 940
Revenues | 139 | 166 | 786 | 940
Natural gas | Residential |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Operating Revenues | 84 | 100 | 543 | 653
Natural gas | Commercial |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Operating Revenues | 24 | 31 | 155 | 188
Natural gas | Industrial |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Operating Revenues | 2 | 6 | 14 | 37
Natural gas | Other |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenues | 29 | 29 | 74 | 62
Ameren Illinois Company |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Operating Revenues | 783 | 904 | 2,663 | 2,697
Revenues | 783 | 904 | 2,663 | 2,697
Revenues from alternative revenue programs | (101) | (96) | 70 | (4)
Other revenues not from contracts with customers | 2 | 2 | 8 | 7
Ameren Illinois Company | Residential |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Operating Revenues | 405 | 496 | 1,518 | 1,529
Ameren Illinois Company | Commercial |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Operating Revenues | 208 | 258 | 703 | 723
Ameren Illinois Company | Industrial |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Operating Revenues | 41 | 52 | 146 | 178
Ameren Illinois Company | Other |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenues | 129 | 98 | 296 | 267
Ameren Illinois Company | Ameren Illinois Electric Distribution |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenues from alternative revenue programs | (94) | (83) | 30 | 13
Other revenues not from contracts with customers | 2 | 2 | 6 | 5
Ameren Illinois Company | Ameren Illinois Natural Gas |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenues from alternative revenue programs | (1) | (3) | 36 | (5)
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 | (6) | (10) | 4 | (12)
Other revenues not from contracts with customers | 0 | 0 | 0 | 0
Ameren Illinois Company | Electric |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Operating Revenues | 661 | 758 | 1,998 | 1,886
Ameren Illinois Company | Natural gas |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Operating Revenues | 122 | 146 | 665 | 811
Operating Segments | Union Electric Company |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Operating Revenues | 1,228 | 1,351 | 3,074 | 3,071
Revenues | 1,237 | 1,359 | 3,101 | 3,096
Operating Segments | Ameren Illinois Electric Distribution |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Operating Revenues | 557 | 672 | 1,721 | 1,640
Revenues | 558 | 672 | 1,722 | 1,641
Operating Segments | Ameren Illinois Natural Gas |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Operating Revenues | 121 | 146 | 664 | 811
Revenues | 122 | 146 | 665 | 811
Operating Segments | Ameren Transmission |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Operating Revenues | 154 | 137 | 423 | 389
Revenues | 188 | 169 | 512 | 465
Operating Segments | Electric | Union Electric Company |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenues | 1,219 | 1,338 | 2,978 | 2,966
Operating Segments | Electric | Union Electric Company | Residential |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Operating Revenues | 590 | 564 | 1,274 | 1,267
Operating Segments | Electric | Union Electric Company | Commercial |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Operating Revenues | 468 | 430 | 1,026 | 968
Operating Segments | Electric | Union Electric Company | Industrial |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Operating Revenues | 107 | 99 | 243 | 229
Operating Segments | Electric | Union Electric Company | Other |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenues | 54 | 245 | 435 | 502
Operating Segments | Electric | Ameren Illinois Electric Distribution |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenues | 558 | 672 | 1,722 | 1,641
Operating Segments | Electric | Ameren Illinois Electric Distribution | Residential |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Operating Revenues | 330 | 407 | 1,049 | 954
Operating Segments | Electric | Ameren Illinois Electric Distribution | Commercial |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Operating Revenues | 189 | 233 | 582 | 571
Operating Segments | Electric | Ameren Illinois Electric Distribution | Industrial |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Operating Revenues | 40 | 47 | 136 | 145
Operating Segments | Electric | Ameren Illinois Electric Distribution | Other |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenues | (1) | (15) | (45) | (29)
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 | 188 | 169 | 512 | 465
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 | 188 | 169 | 512 | 465
Operating Segments | Natural gas | Union Electric Company |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenues | 18 | 21 | 123 | 130
Operating Segments | Natural gas | Union Electric Company | Residential |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Operating Revenues | 9 | 11 | 74 | 78
Operating Segments | Natural gas | Union Electric Company | Commercial |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Operating Revenues | 5 | 6 | 34 | 36
Operating Segments | Natural gas | Union Electric Company | Industrial |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Operating Revenues | 1 | 1 | 4 | 4
Operating Segments | Natural gas | Union Electric Company | Other |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenues | 3 | 3 | 11 | 12
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 | 122 | 146 | 665 | 811
Operating Segments | Natural gas | Ameren Illinois Natural Gas | Residential |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Operating Revenues | 75 | 89 | 469 | 575
Operating Segments | Natural gas | Ameren Illinois Natural Gas | Commercial |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Operating Revenues | 19 | 25 | 121 | 152
Operating Segments | Natural gas | Ameren Illinois Natural Gas | Industrial |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Operating Revenues | 1 | 5 | 10 | 33
Operating Segments | Natural gas | Ameren Illinois Natural Gas | Other |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenues | 27 | 27 | 65 | 51
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 | 558 | 672 | 1,722 | 1,641
Operating Segments | Ameren Illinois Company | Ameren Illinois Natural Gas |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Operating Revenues | 122 | 146 | 665 | 811
Operating Segments | Ameren Illinois Company | Ameren Illinois Transmission |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Operating Revenues | 103 | 86 | 276 | 245
Operating Segments | Ameren Illinois Company | Electric | Ameren Illinois Electric Distribution |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenues | 558 | 672 | 1,722 | 1,641
Operating Segments | Ameren Illinois Company | Electric | Ameren Illinois Electric Distribution | Residential |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Operating Revenues | 330 | 407 | 1,049 | 954
Operating Segments | Ameren Illinois Company | Electric | Ameren Illinois Electric Distribution | Commercial |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Operating Revenues | 189 | 233 | 582 | 571
Operating Segments | Ameren Illinois Company | Electric | Ameren Illinois Electric Distribution | Industrial |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Operating Revenues | 40 | 47 | 136 | 145
Operating Segments | Ameren Illinois Company | Electric | Ameren Illinois Electric Distribution | Other |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenues | (1) | (15) | (45) | (29)
Operating Segments | Ameren Illinois Company | Electric | Ameren Illinois Transmission |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenues | 136 | 117 | 363 | 320
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 | 136 | 117 | 363 | 320
Operating Segments | Ameren Illinois Company | Natural gas | Ameren Illinois Natural Gas |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenues | 122 | 146 | 665 | 811
Operating Segments | Ameren Illinois Company | Natural gas | Ameren Illinois Natural Gas | Residential |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Operating Revenues | 75 | 89 | 469 | 575
Operating Segments | Ameren Illinois Company | Natural gas | Ameren Illinois Natural Gas | Commercial |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Operating Revenues | 19 | 25 | 121 | 152
Operating Segments | Ameren Illinois Company | Natural gas | Ameren Illinois Natural Gas | Industrial |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Operating Revenues | 1 | 5 | 10 | 33
Operating Segments | Ameren Illinois Company | Natural gas | Ameren Illinois Natural Gas | Other |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenues | 27 | 27 | 65 | 51
Intersegment Eliminations |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenues | (45) | (40) | (118) | (102)
Revenues | (45) | (40) | (118) | (102)
Intersegment Eliminations | Union Electric Company |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenues | (9) | (8) | (27) | (25)
Intersegment Eliminations | Ameren Illinois Electric Distribution |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenues | (1) | 0 | (1) | (1)
Intersegment Eliminations | Ameren Illinois Natural Gas |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenues | (1) | 0 | (1) | 0
Intersegment Eliminations | Ameren Transmission |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenues | (34) | (32) | (89) | (76)
Intersegment Eliminations | Electric |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenues | (44) | (39) | (116) | (101)
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 | (44) | (39) | (116) | (101)
Intersegment Eliminations | Natural gas |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenues | (1) | (1) | (2) | (1)
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) | (2) | (1)
Intersegment Eliminations | Ameren Illinois Company |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenues | (33) | (31) | (87) | (75)
Revenues | (33) | (31) | (87) | (75)
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 | (33) | (31) | (87) | (75)
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 | $ (33) | $ (31) | $ (87) | $ (75)

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