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Segment Information (Disaggregation of Revenue) (Details) - USD ($) $ in Millions | 3 Months Ended | 6 Months Ended
--- | --- | ---
Jun. 30, 2024 | Jun. 30, 2023 | Jun. 30, 2024 | Jun. 30, 2023
Disaggregation of Revenue [Line Items] |  |  |  |
Operating Revenues | $ 1,693 | $ 1,760 | $ 3,509 | $ 3,822
Revenues | 1,693 | 1,760 | 3,509 | 3,822
Revenues from alternative revenue programs | 25 | 74 | 86 | 172
Other revenues not from contracts with customers | 3 | 1 | 7 | (2)
Union Electric Company |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenues from alternative revenue programs | (1) | 0 | (7) | (2)
Other revenues not from contracts with customers | 1 | (2) | 2 | (8)
Ameren Illinois Electric Distribution |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenues from alternative revenue programs | 22 | 60 | 61 | 124
Other revenues not from contracts with customers | 1 | 2 | 3 | 4
Ameren Illinois Natural Gas |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenues from alternative revenue programs | 0 | 9 | 19 | 37
Other revenues not from contracts with customers | 1 | 1 | 2 | 2
Ameren Transmission |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenues from alternative revenue programs | 4 | 5 | 13 | 13
Other revenues not from contracts with customers | 0 | 0 | 0 | 0
Electric |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Operating Revenues | 1,521 | 1,585 | 2,885 | 3,175
Revenues | 1,521 | 1,585 | 2,885 | 3,175
Electric | Residential |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Operating Revenues | 706 | 697 | 1,344 | 1,403
Electric | Commercial |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Operating Revenues | 487 | 504 | 911 | 951
Electric | Industrial |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Operating Revenues | 124 | 123 | 230 | 232
Electric | Other |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenues | 204 | 261 | 400 | 589
Natural gas |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Operating Revenues | 172 | 175 | 624 | 647
Revenues | 172 | 175 | 624 | 647
Natural gas | Residential |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Operating Revenues | 115 | 111 | 442 | 459
Natural gas | Commercial |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Operating Revenues | 29 | 31 | 113 | 131
Natural gas | Industrial |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Operating Revenues | 2 | 3 | 8 | 12
Natural gas | Other |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenues | 26 | 30 | 61 | 45
Ameren Illinois Company |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Operating Revenues | 766 | 779 | 1,766 | 1,880
Revenues | 766 | 779 | 1,766 | 1,880
Revenues from alternative revenue programs | 24 | 72 | 90 | 171
Other revenues not from contracts with customers | 2 | 3 | 5 | 6
Ameren Illinois Company | Residential |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Operating Revenues | 413 | 435 | 997 | 1,113
Ameren Illinois Company | Commercial |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Operating Revenues | 187 | 218 | 420 | 495
Ameren Illinois Company | Industrial |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Operating Revenues | 48 | 50 | 97 | 105
Ameren Illinois Company | Other |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenues | 118 | 76 | 252 | 167
Ameren Illinois Company | Ameren Illinois Electric Distribution |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenues from alternative revenue programs | 22 | 60 | 61 | 124
Other revenues not from contracts with customers | 1 | 2 | 3 | 4
Ameren Illinois Company | Ameren Illinois Natural Gas |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenues from alternative revenue programs | 0 | 9 | 19 | 37
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 | 2 | 3 | 10 | 10
Other revenues not from contracts with customers | 0 | 0 | 0 | 0
Ameren Illinois Company | Electric |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Operating Revenues | 618 | 627 | 1,227 | 1,337
Ameren Illinois Company | Natural gas |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Operating Revenues | 148 | 152 | 539 | 543
Operating Segments | Union Electric Company |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Operating Revenues | 879 | 933 | 1,647 | 1,846
Revenues | 888 | 941 | 1,663 | 1,864
Operating Segments | Ameren Illinois Electric Distribution |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Operating Revenues | 509 | 540 | 1,015 | 1,164
Revenues | 509 | 540 | 1,015 | 1,164
Operating Segments | Ameren Illinois Natural Gas |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Operating Revenues | 148 | 152 | 539 | 543
Revenues | 148 | 152 | 539 | 543
Operating Segments | Ameren Transmission |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Operating Revenues | 157 | 135 | 308 | 269
Revenues | 191 | 161 | 376 | 324
Operating Segments | Electric | Union Electric Company |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenues | 864 | 918 | 1,578 | 1,759
Operating Segments | Electric | Union Electric Company | Residential |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Operating Revenues | 395 | 360 | 736 | 684
Operating Segments | Electric | Union Electric Company | Commercial |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Operating Revenues | 324 | 311 | 583 | 558
Operating Segments | Electric | Union Electric Company | Industrial |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Operating Revenues | 77 | 75 | 138 | 136
Operating Segments | Electric | Union Electric Company | Other |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenues | 68 | 172 | 121 | 381
Operating Segments | Electric | Ameren Illinois Electric Distribution |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenues | 509 | 540 | 1,015 | 1,164
Operating Segments | Electric | Ameren Illinois Electric Distribution | Residential |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Operating Revenues | 311 | 337 | 608 | 719
Operating Segments | Electric | Ameren Illinois Electric Distribution | Commercial |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Operating Revenues | 163 | 193 | 328 | 393
Operating Segments | Electric | Ameren Illinois Electric Distribution | Industrial |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Operating Revenues | 47 | 48 | 92 | 96
Operating Segments | Electric | Ameren Illinois Electric Distribution | Other |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenues | (12) | (38) | (13) | (44)
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 | 191 | 161 | 376 | 324
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 | 191 | 161 | 376 | 324
Operating Segments | Natural gas | Union Electric Company |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenues | 24 | 23 | 85 | 105
Operating Segments | Natural gas | Union Electric Company | Residential |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Operating Revenues | 13 | 13 | 53 | 65
Operating Segments | Natural gas | Union Electric Company | Commercial |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Operating Revenues | 5 | 6 | 21 | 29
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 | 5 | 3 | 8 | 8
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 | 148 | 152 | 539 | 543
Operating Segments | Natural gas | Ameren Illinois Natural Gas | Residential |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Operating Revenues | 102 | 98 | 389 | 394
Operating Segments | Natural gas | Ameren Illinois Natural Gas | Commercial |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Operating Revenues | 24 | 25 | 92 | 102
Operating Segments | Natural gas | Ameren Illinois Natural Gas | Industrial |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Operating Revenues | 1 | 2 | 5 | 9
Operating Segments | Natural gas | Ameren Illinois Natural Gas | Other |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenues | 21 | 27 | 53 | 38
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 | 509 | 540 | 1,015 | 1,164
Operating Segments | Ameren Illinois Company | Ameren Illinois Natural Gas |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Operating Revenues | 148 | 152 | 539 | 543
Operating Segments | Ameren Illinois Company | Ameren Illinois Transmission |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Operating Revenues | 109 | 87 | 212 | 173
Operating Segments | Ameren Illinois Company | Electric | Ameren Illinois Electric Distribution |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenues | 509 | 540 | 1,015 | 1,164
Operating Segments | Ameren Illinois Company | Electric | Ameren Illinois Electric Distribution | Residential |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Operating Revenues | 311 | 337 | 608 | 719
Operating Segments | Ameren Illinois Company | Electric | Ameren Illinois Electric Distribution | Commercial |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Operating Revenues | 163 | 193 | 328 | 393
Operating Segments | Ameren Illinois Company | Electric | Ameren Illinois Electric Distribution | Industrial |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Operating Revenues | 47 | 48 | 92 | 96
Operating Segments | Ameren Illinois Company | Electric | Ameren Illinois Electric Distribution | Other |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenues | (12) | (38) | (13) | (44)
Operating Segments | Ameren Illinois Company | Electric | Ameren Illinois Transmission |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenues | 136 | 113 | 267 | 227
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 | 113 | 267 | 227
Operating Segments | Ameren Illinois Company | Natural gas | Ameren Illinois Natural Gas |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenues | 148 | 152 | 539 | 543
Operating Segments | Ameren Illinois Company | Natural gas | Ameren Illinois Natural Gas | Residential |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Operating Revenues | 102 | 98 | 389 | 394
Operating Segments | Ameren Illinois Company | Natural gas | Ameren Illinois Natural Gas | Commercial |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Operating Revenues | 24 | 25 | 92 | 102
Operating Segments | Ameren Illinois Company | Natural gas | Ameren Illinois Natural Gas | Industrial |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Operating Revenues | 1 | 2 | 5 | 9
Operating Segments | Ameren Illinois Company | Natural gas | Ameren Illinois Natural Gas | Other |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenues | 21 | 27 | 53 | 38
Intersegment Eliminations |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenues | (43) | (34) | (84) | (73)
Revenues | (43) | (34) | (84) | (73)
Intersegment Eliminations | Union Electric Company |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenues | (9) | (8) | (16) | (18)
Intersegment Eliminations | Ameren Illinois Electric Distribution |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenues | 0 | 0 | 0 | 0
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 | (34) | (26) | (68) | (55)
Intersegment Eliminations | Electric |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenues | (43) | (34) | (84) | (72)
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 | (43) | (34) | (84) | (72)
Intersegment Eliminations | Natural gas |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenues | 0 | 0 | 0 | (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 | 0 | 0 | 0 | (1)
Intersegment Eliminations | Ameren Illinois Company |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenues | (27) | (26) | (55) | (54)
Revenues | (27) | (26) | (55) | (54)
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 | (27) | (26) | (55) | (54)
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 | $ (27) | $ (26) | $ (55) | $ (54)

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