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Revenue Recognition (Disaggregation of Revenue) (Details) - USD ($) $ in Millions | 12 Months Ended
--- | ---
Dec. 31, 2021 | Dec. 31, 2020 | Dec. 31, 2019
Disaggregation of Revenue [Line Items] |  |  |
Customer revenues | $ 4,731.3 | $ 4,473.2 | $ 5,053.4
Other revenues | 168.3 | 208.5 | 155.5
Total Operating Revenues | 4,899.6 | 4,681.7 | 5,208.9
Gas Distribution Operations |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Customer revenues | 3,126.1 | 3,032.0 | 3,455.2
Other revenues | 45.1 | 96.1 | 54.5
Total Operating Revenues | 3,171.2 | 3,128.1 | 3,509.7
Electric Operations |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Customer revenues | 1,604.4 | 1,440.4 | 1,597.4
Other revenues | 91.9 | 95.5 | 101.0
Total Operating Revenues | 1,696.3 | 1,535.9 | 1,698.4
Corporate and Other |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Customer revenues | 0.8 | 0.8 | 0.8
Other revenues | 31.3 | 16.9 | 0.0
Total Operating Revenues | 32.1 | 17.7 | 0.8
Residential |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Customer revenues | 2,677.3 | 2,602.8 | 2,790.6
Residential | Gas Distribution Operations |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Customer revenues | 2,109.4 | 2,075.0 | 2,309.0
Residential | Electric Operations |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Customer revenues | 567.9 | 527.8 | 481.6
Residential | Corporate and Other |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Customer revenues | 0.0 | 0.0 | 0.0
Commercial |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Customer revenues | 1,257.3 | 1,150.8 | 1,257.9
Commercial | Gas Distribution Operations |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Customer revenues | 722.4 | 670.5 | 771.3
Commercial | Electric Operations |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Customer revenues | 534.9 | 480.3 | 486.6
Commercial | Corporate and Other |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Customer revenues | 0.0 | 0.0 | 0.0
Industrial |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Customer revenues | 689.1 | 624.9 | 852.9
Industrial | Gas Distribution Operations |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Customer revenues | 195.7 | 212.8 | 245.2
Industrial | Electric Operations |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Customer revenues | 493.4 | 412.1 | 607.7
Industrial | Corporate and Other |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Customer revenues | 0.0 | 0.0 | 0.0
Off-system |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Customer revenues | 71.3 | 41.0 | 77.7
Off-system | Gas Distribution Operations |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Customer revenues | 71.3 | 41.0 | 77.7
Off-system | Electric Operations |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Customer revenues | 0.0 | 0.0 | 0.0
Off-system | Corporate and Other |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Customer revenues | 0.0 | 0.0 | 0.0
Miscellaneous |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Customer revenues | 36.3 | 53.7 | 74.3
Miscellaneous | Gas Distribution Operations |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Customer revenues | 27.3 | 32.7 | 52.0
Miscellaneous | Electric Operations |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Customer revenues | 8.2 | 20.2 | 21.5
Miscellaneous | Corporate and Other |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Customer revenues | $ 0.8 | $ 0.8 | $ 0.8

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