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Segment Information (Disaggregation of Revenues) (Details) - USD ($) $ in Millions | 12 Months Ended
--- | ---
Dec. 31, 2022 | Dec. 31, 2021 | Dec. 31, 2020
Disaggregation of Revenue [Line Items] |  |  |
External revenues | $ 7,957 | $ 6,394 | $ 5,794
Revenues from alternative revenue programs | 78 | 77 | 36
Revenue Not from Contract with Customer, Other | (94) | 68 | 36
Revenues | 7,957 | 6,394 | 5,794
Union Electric Company |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Revenues from alternative revenue programs | 17 | (16) | (14)
Revenue Not from Contract with Customer, Other | (103) | 56 | 25
Ameren Illinois Electric Distribution |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Revenues from alternative revenue programs | 89 | 77 | (20)
Revenue Not from Contract with Customer, Other | 6 | 10 | 8
Ameren Illinois Gas |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Revenues from alternative revenue programs | (19) | 5 | 20
Revenue Not from Contract with Customer, Other | 3 | 2 | 2
Ameren Transmission |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Revenues from alternative revenue programs | (9) | 11 | 50
Revenue Not from Contract with Customer, Other | 0 | 0 | 1
Electric |  |  |
Disaggregation of Revenue [Line Items] |  |  |
External revenues | 6,581 | 5,297 | 4,911
Revenues | 6,581 | 5,297 | 4,911
Electric | Residential |  |  |
Disaggregation of Revenue [Line Items] |  |  |
External revenues | 2,903 | 2,378 | 2,240
Electric | Commercial |  |  |
Disaggregation of Revenue [Line Items] |  |  |
External revenues | 1,987 | 1,671 | 1,511
Electric | Industrial |  |  |
Disaggregation of Revenue [Line Items] |  |  |
External revenues | 489 | 415 | 385
Electric | Other |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Revenue Not from Contract with Customer | 1,202 | 833 | 775
Natural gas |  |  |
Disaggregation of Revenue [Line Items] |  |  |
External revenues | 1,376 | 1,097 | 883
Revenues | 1,376 | 1,097 | 883
Natural gas | Residential |  |  |
Disaggregation of Revenue [Line Items] |  |  |
External revenues | 965 | 736 | 617
Natural gas | Commercial |  |  |
Disaggregation of Revenue [Line Items] |  |  |
External revenues | 277 | 206 | 165
Natural gas | Industrial |  |  |
Disaggregation of Revenue [Line Items] |  |  |
External revenues | 48 | 39 | 18
Natural gas | Other |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Revenue Not from Contract with Customer | 86 | 116 | 83
Ameren Illinois Company |  |  |
Disaggregation of Revenue [Line Items] |  |  |
External revenues | 3,756 | 2,895 | 2,535
Revenues from alternative revenue programs | 63 | 91 | 42
Revenue Not from Contract with Customer, Other | 9 | 12 | 10
Revenues | 3,756 | 2,895 | 2,535
Ameren Illinois Company | Residential |  |  |
Disaggregation of Revenue [Line Items] |  |  |
External revenues | 2,171 | 1,590 | 1,408
Ameren Illinois Company | Commercial |  |  |
Disaggregation of Revenue [Line Items] |  |  |
External revenues | 989 | 717 | 622
Ameren Illinois Company | Industrial |  |  |
Disaggregation of Revenue [Line Items] |  |  |
External revenues | 240 | 170 | 138
Ameren Illinois Company | Other |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Revenue Not from Contract with Customer | 356 | 418 | 367
Ameren Illinois Company | Ameren Illinois Electric Distribution |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Revenues from alternative revenue programs | 89 | 77 | (20)
Revenue Not from Contract with Customer, Other | 6 | 10 | 8
Ameren Illinois Company | Ameren Illinois Gas |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Revenues from alternative revenue programs | (19) | 5 | 20
Revenue Not from Contract with Customer, Other | 3 | 2 | 2
Ameren Illinois Company | Ameren Illinois Transmission |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Revenues from alternative revenue programs | (7) | 9 | 42
Revenue Not from Contract with Customer, Other | 0 | 0 | 0
Ameren Illinois Company | Electric |  |  |
Disaggregation of Revenue [Line Items] |  |  |
External revenues | 2,576 | 1,938 | 1,775
Ameren Illinois Company | Natural gas |  |  |
Disaggregation of Revenue [Line Items] |  |  |
External revenues | 1,180 | 957 | 760
Operating Segments | Union Electric Company |  |  |
Disaggregation of Revenue [Line Items] |  |  |
External revenues | 4,012 | 3,311 | 3,069
Revenues | 4,046 | 3,353 | 3,109
Operating Segments | Ameren Illinois Electric Distribution |  |  |
Disaggregation of Revenue [Line Items] |  |  |
External revenues | 2,255 | 1,635 | 1,496
Revenues | 2,256 | 1,639 | 1,498
Operating Segments | Ameren Illinois Gas |  |  |
Disaggregation of Revenue [Line Items] |  |  |
External revenues | 1,180 | 957 | 760
Revenues | 1,180 | 957 | 760
Operating Segments | Ameren Transmission |  |  |
Disaggregation of Revenue [Line Items] |  |  |
External revenues | 510 | 491 | 469
Revenues | 615 | 562 | 523
Operating Segments | Electric | Union Electric Company |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Revenues | 3,849 | 3,212 | 2,984
Operating Segments | Electric | Union Electric Company | Residential |  |  |
Disaggregation of Revenue [Line Items] |  |  |
External revenues | 1,578 | 1,445 | 1,373
Operating Segments | Electric | Union Electric Company | Commercial |  |  |
Disaggregation of Revenue [Line Items] |  |  |
External revenues | 1,219 | 1,126 | 1,025
Operating Segments | Electric | Union Electric Company | Industrial |  |  |
Disaggregation of Revenue [Line Items] |  |  |
External revenues | 290 | 280 | 261
Operating Segments | Electric | Union Electric Company | Other |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Revenue Not from Contract with Customer | 762 | 361 | 325
Operating Segments | Electric | Ameren Illinois Electric Distribution |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Revenues | 2,256 | 1,639 | 1,498
Operating Segments | Electric | Ameren Illinois Electric Distribution | Residential |  |  |
Disaggregation of Revenue [Line Items] |  |  |
External revenues | 1,325 | 933 | 867
Operating Segments | Electric | Ameren Illinois Electric Distribution | Commercial |  |  |
Disaggregation of Revenue [Line Items] |  |  |
External revenues | 768 | 545 | 486
Operating Segments | Electric | Ameren Illinois Electric Distribution | Industrial |  |  |
Disaggregation of Revenue [Line Items] |  |  |
External revenues | 199 | 135 | 124
Operating Segments | Electric | Ameren Illinois Electric Distribution | Other |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Revenue Not from Contract with Customer | (36) | 26 | 21
Operating Segments | Electric | Ameren Illinois Gas |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Revenues | 0 | 0 | 0
Operating Segments | Electric | Ameren Illinois Gas | Residential |  |  |
Disaggregation of Revenue [Line Items] |  |  |
External revenues | 0 | 0 | 0
Operating Segments | Electric | Ameren Illinois Gas | Commercial |  |  |
Disaggregation of Revenue [Line Items] |  |  |
External revenues | 0 | 0 | 0
Operating Segments | Electric | Ameren Illinois Gas | Industrial |  |  |
Disaggregation of Revenue [Line Items] |  |  |
External revenues | 0 | 0 | 0
Operating Segments | Electric | Ameren Illinois Gas | Other |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Revenue Not from Contract with Customer | 0 | 0 | 0
Operating Segments | Electric | Ameren Transmission |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Revenues | 615 | 562 | 523
Operating Segments | Electric | Ameren Transmission | Residential |  |  |
Disaggregation of Revenue [Line Items] |  |  |
External revenues | 0 | 0 | 0
Operating Segments | Electric | Ameren Transmission | Commercial |  |  |
Disaggregation of Revenue [Line Items] |  |  |
External revenues | 0 | 0 | 0
Operating Segments | Electric | Ameren Transmission | Industrial |  |  |
Disaggregation of Revenue [Line Items] |  |  |
External revenues | 0 | 0 | 0
Operating Segments | Electric | Ameren Transmission | Other |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Revenue Not from Contract with Customer | 615 | 562 | 523
Operating Segments | Natural gas | Union Electric Company |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Revenues | 197 | 141 | 125
Operating Segments | Natural gas | Union Electric Company | Residential |  |  |
Disaggregation of Revenue [Line Items] |  |  |
External revenues | 119 | 79 | 76
Operating Segments | Natural gas | Union Electric Company | Commercial |  |  |
Disaggregation of Revenue [Line Items] |  |  |
External revenues | 56 | 34 | 29
Operating Segments | Natural gas | Union Electric Company | Industrial |  |  |
Disaggregation of Revenue [Line Items] |  |  |
External revenues | 7 | 4 | 4
Operating Segments | Natural gas | Union Electric Company | Other |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Revenue Not from Contract with Customer | 15 | 24 | 16
Operating Segments | Natural gas | Ameren Illinois Electric Distribution |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Revenues | 0 | 0 | 0
Operating Segments | Natural gas | Ameren Illinois Electric Distribution | Residential |  |  |
Disaggregation of Revenue [Line Items] |  |  |
External revenues | 0 | 0 | 0
Operating Segments | Natural gas | Ameren Illinois Electric Distribution | Commercial |  |  |
Disaggregation of Revenue [Line Items] |  |  |
External revenues | 0 | 0 | 0
Operating Segments | Natural gas | Ameren Illinois Electric Distribution | Industrial |  |  |
Disaggregation of Revenue [Line Items] |  |  |
External revenues | 0 | 0 | 0
Operating Segments | Natural gas | Ameren Illinois Electric Distribution | Other |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Revenue Not from Contract with Customer | 0 | 0 | 0
Operating Segments | Natural gas | Ameren Illinois Gas |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Revenues | 1,180 | 957 | 760
Operating Segments | Natural gas | Ameren Illinois Gas | Residential |  |  |
Disaggregation of Revenue [Line Items] |  |  |
External revenues | 846 | 657 | 541
Operating Segments | Natural gas | Ameren Illinois Gas | Commercial |  |  |
Disaggregation of Revenue [Line Items] |  |  |
External revenues | 221 | 172 | 136
Operating Segments | Natural gas | Ameren Illinois Gas | Industrial |  |  |
Disaggregation of Revenue [Line Items] |  |  |
External revenues | 41 | 35 | 14
Operating Segments | Natural gas | Ameren Illinois Gas | Other |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Revenue Not from Contract with Customer | 72 | 93 | 69
Operating Segments | Natural gas | Ameren Transmission |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Revenues | 0 | 0 | 0
Operating Segments | Natural gas | Ameren Transmission | Residential |  |  |
Disaggregation of Revenue [Line Items] |  |  |
External revenues | 0 | 0 | 0
Operating Segments | Natural gas | Ameren Transmission | Commercial |  |  |
Disaggregation of Revenue [Line Items] |  |  |
External revenues | 0 | 0 | 0
Operating Segments | Natural gas | Ameren Transmission | Industrial |  |  |
Disaggregation of Revenue [Line Items] |  |  |
External revenues | 0 | 0 | 0
Operating Segments | Natural gas | Ameren Transmission | Other |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Revenue Not from Contract with Customer | 0 | 0 | 0
Operating Segments | Ameren Illinois Company | Ameren Illinois Electric Distribution |  |  |
Disaggregation of Revenue [Line Items] |  |  |
External revenues | 2,256 | 1,639 | 1,498
Operating Segments | Ameren Illinois Company | Ameren Illinois Gas |  |  |
Disaggregation of Revenue [Line Items] |  |  |
External revenues | 1,180 | 957 | 760
Operating Segments | Ameren Illinois Company | Ameren Illinois Transmission |  |  |
Disaggregation of Revenue [Line Items] |  |  |
External revenues | 320 | 299 | 277
Operating Segments | Ameren Illinois Company | Electric | Ameren Illinois Electric Distribution |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Revenues | 2,256 | 1,639 | 1,498
Operating Segments | Ameren Illinois Company | Electric | Ameren Illinois Electric Distribution | Residential |  |  |
Disaggregation of Revenue [Line Items] |  |  |
External revenues | 1,325 | 933 | 867
Operating Segments | Ameren Illinois Company | Electric | Ameren Illinois Electric Distribution | Commercial |  |  |
Disaggregation of Revenue [Line Items] |  |  |
External revenues | 768 | 545 | 486
Operating Segments | Ameren Illinois Company | Electric | Ameren Illinois Electric Distribution | Industrial |  |  |
Disaggregation of Revenue [Line Items] |  |  |
External revenues | 199 | 135 | 124
Operating Segments | Ameren Illinois Company | Electric | Ameren Illinois Electric Distribution | Other |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Revenue Not from Contract with Customer | (36) | 26 | 21
Operating Segments | Ameren Illinois Company | Electric | Ameren Illinois Transmission |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Revenues | 424 | 365 | 329
Operating Segments | Ameren Illinois Company | Electric | Ameren Illinois Transmission | Residential |  |  |
Disaggregation of Revenue [Line Items] |  |  |
External revenues | 0 | 0 | 0
Operating Segments | Ameren Illinois Company | Electric | Ameren Illinois Transmission | Commercial |  |  |
Disaggregation of Revenue [Line Items] |  |  |
External revenues | 0 | 0 | 0
Operating Segments | Ameren Illinois Company | Electric | Ameren Illinois Transmission | Industrial |  |  |
Disaggregation of Revenue [Line Items] |  |  |
External revenues | 0 | 0 | 0
Operating Segments | Ameren Illinois Company | Electric | Ameren Illinois Transmission | Other |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Revenue Not from Contract with Customer | 424 | 365 | 329
Operating Segments | Ameren Illinois Company | Natural gas | Ameren Illinois Gas |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Revenues | 1,180 | 957 | 760
Operating Segments | Ameren Illinois Company | Natural gas | Ameren Illinois Gas | Residential |  |  |
Disaggregation of Revenue [Line Items] |  |  |
External revenues | 846 | 657 | 541
Operating Segments | Ameren Illinois Company | Natural gas | Ameren Illinois Gas | Commercial |  |  |
Disaggregation of Revenue [Line Items] |  |  |
External revenues | 221 | 172 | 136
Operating Segments | Ameren Illinois Company | Natural gas | Ameren Illinois Gas | Industrial |  |  |
Disaggregation of Revenue [Line Items] |  |  |
External revenues | 41 | 35 | 14
Operating Segments | Ameren Illinois Company | Natural gas | Ameren Illinois Gas | Other |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Revenue Not from Contract with Customer | 72 | 93 | 69
Intersegment Elimination |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Revenue Not from Contract with Customer | (140) | (117) | (96)
Revenues | (140) | (117) | (96)
Intersegment Elimination | Union Electric Company |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Revenue Not from Contract with Customer | (34) | (42) | (40)
Intersegment Elimination | Ameren Illinois Electric Distribution |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Revenue Not from Contract with Customer | (1) | (4) | (2)
Intersegment Elimination | Ameren Illinois Gas |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Revenue Not from Contract with Customer | 0 | 0 | 0
Intersegment Elimination | Ameren Transmission |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Revenue Not from Contract with Customer | (105) | (71) | (54)
Intersegment Elimination | Electric |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Revenues | (139) | (116) | (94)
Intersegment Elimination | Electric | Residential |  |  |
Disaggregation of Revenue [Line Items] |  |  |
External revenues | 0 | 0 | 0
Intersegment Elimination | Electric | Commercial |  |  |
Disaggregation of Revenue [Line Items] |  |  |
External revenues | 0 | 0 | 0
Intersegment Elimination | Electric | Industrial |  |  |
Disaggregation of Revenue [Line Items] |  |  |
External revenues | 0 | 0 | 0
Intersegment Elimination | Electric | Other |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Revenue Not from Contract with Customer | (139) | (116) | (94)
Intersegment Elimination | Natural gas |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Revenues | (1) | (1) | (2)
Intersegment Elimination | Natural gas | Residential |  |  |
Disaggregation of Revenue [Line Items] |  |  |
External revenues | 0 | 0 | 0
Intersegment Elimination | Natural gas | Commercial |  |  |
Disaggregation of Revenue [Line Items] |  |  |
External revenues | 0 | 0 | 0
Intersegment Elimination | Natural gas | Industrial |  |  |
Disaggregation of Revenue [Line Items] |  |  |
External revenues | 0 | 0 | 0
Intersegment Elimination | Natural gas | Other |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Revenue Not from Contract with Customer | (1) | (1) | (2)
Intersegment Elimination | Ameren Illinois Company |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Revenue Not from Contract with Customer | (104) | (66) | (52)
Revenues | (104) | (66) | (52)
Intersegment Elimination | Ameren Illinois Company | Residential |  |  |
Disaggregation of Revenue [Line Items] |  |  |
External revenues | 0 | 0 | 0
Intersegment Elimination | Ameren Illinois Company | Commercial |  |  |
Disaggregation of Revenue [Line Items] |  |  |
External revenues | 0 | 0 | 0
Intersegment Elimination | Ameren Illinois Company | Industrial |  |  |
Disaggregation of Revenue [Line Items] |  |  |
External revenues | 0 | 0 | 0
Intersegment Elimination | Ameren Illinois Company | Other |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Revenue Not from Contract with Customer | (104) | (66) | (52)
Intersegment Elimination | Ameren Illinois Company | Ameren Illinois Electric Distribution |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Revenue Not from Contract with Customer | 0 | 0 | 0
Intersegment Elimination | Ameren Illinois Company | Ameren Illinois Gas |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Revenue Not from Contract with Customer | 0 | 0 | 0
Intersegment Elimination | Ameren Illinois Company | Ameren Illinois Transmission |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Revenue Not from Contract with Customer | $ (104) | $ (66) | $ (52)

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- Definition Amount of revenue recognized from goods sold, services rendered, insurance premiums, or other activities that constitute an earning process. 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