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Revenue Recognition (Disaggregation of Revenue) (Details) - USD ($) $ in Millions | 3 Months Ended | 9 Months Ended
--- | --- | ---
Sep. 30, 2020 | Sep. 30, 2019 | Sep. 30, 2020 | Sep. 30, 2019
Disaggregation of Revenue [Line Items] |  |  |  |  |
Customer revenues | [1] | $ 861.5 | $ 891.0 | $ 3,320.1 | $ 3,694.7
Other revenues |  | 41.0 | 40.5 | 150.6 | 117.0
Total Operating Revenues |  | 902.5 | 931.5 | 3,470.7 | 3,811.7
Gas Distribution Operations |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |
Customer revenues | [1] | 454.3 | 451.2 | 2,224.9 | 2,462.7
Other revenues |  | 15.8 | 12.4 | 79.5 | 43.5
Total Operating Revenues |  | 470.1 | 463.6 | 2,304.4 | 2,506.2
Electric Operations |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |
Customer revenues | [1] | 407.0 | 439.6 | 1,094.6 | 1,231.4
Other revenues |  | 25.2 | 28.1 | 71.1 | 73.5
Total Operating Revenues |  | 432.2 | 467.7 | 1,165.7 | 1,304.9
Corporate and Other |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |
Customer revenues | [1] | 0.2 | 0.2 | 0.6 | 0.6
Other revenues |  | 0.0 | 0.0 | 0.0 | 0.0
Total Operating Revenues |  | 0.2 | 0.2 | 0.6 | 0.6
Residential |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |
Customer revenues | [1] | 471.7 | 437.0 | 1,929.6 | 2,012.0
Residential | Gas Distribution Operations |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |
Customer revenues | [1] | 306.9 | 288.3 | 1,518.1 | 1,638.6
Residential | Electric Operations |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |
Customer revenues | [1] | 164.8 | 148.7 | 411.5 | 373.4
Residential | Corporate and Other |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |
Customer revenues | [1] | 0.0 | 0.0 | 0.0 | 0.0
Commercial |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |
Customer revenues | [1] | 224.1 | 227.2 | 849.3 | 913.9
Commercial | Gas Distribution Operations |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |
Customer revenues | [1] | 91.8 | 90.9 | 483.9 | 543.2
Commercial | Electric Operations |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |
Customer revenues | [1] | 132.3 | 136.3 | 365.4 | 370.7
Commercial | Corporate and Other |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |
Customer revenues | [1] | 0.0 | 0.0 | 0.0 | 0.0
Industrial |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |
Customer revenues | [1] | 145.5 | 196.8 | 466.7 | 651.7
Industrial | Gas Distribution Operations |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |
Customer revenues | [1] | 42.8 | 45.3 | 165.6 | 181.1
Industrial | Electric Operations |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |
Customer revenues | [1] | 102.7 | 151.5 | 301.1 | 470.6
Industrial | Corporate and Other |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |
Customer revenues | [1] | 0.0 | 0.0 | 0.0 | 0.0
Off-system |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |
Customer revenues | [1] | 6.0 | 16.9 | 32.7 | 60.4
Off-system | Gas Distribution Operations |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |
Customer revenues | [1] | 6.0 | 16.9 | 32.7 | 60.4
Off-system | Electric Operations |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |
Customer revenues | [1] | 0.0 | 0.0 | 0.0 | 0.0
Off-system | Corporate and Other |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |
Customer revenues | [1] | 0.0 | 0.0 | 0.0 | 0.0
Miscellaneous |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |
Customer revenues | [1] | 14.2 | 13.1 | 41.8 | 56.7
Miscellaneous | Gas Distribution Operations |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |
Customer revenues | [1] | 6.8 | 9.8 | 24.6 | 39.4
Miscellaneous | Electric Operations |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |
Customer revenues | [1] | 7.2 | 3.1 | 16.6 | 16.7
Miscellaneous | Corporate and Other |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |
Customer revenues | [1] | $ 0.2 | $ 0.2 | $ 0.6 | $ 0.6
[1] | Customer revenue amounts exclude intersegment revenues. See Note 21, "Business Segment Information," for discussion of intersegment revenues.

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