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Revenue Recognition (Disaggregation of Revenue) (Details) - USD ($) $ in Millions | 3 Months Ended
--- | ---
Mar. 31, 2020 | Mar. 31, 2019
Disaggregation of Revenue [Line Items] |  |  |
Customer revenues | [1] | $ 1,525.9 | $ 1,834.5
Other revenues |  | 79.6 | 35.3
Total Operating Revenues |  | 1,605.5 | 1,869.8
Gas Distribution Operations |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Customer revenues | [1] | 1,171.3 | 1,426.0
Other revenues |  | 56.7 | 12.8
Total Operating Revenues |  | 1,228.0 | 1,438.8
Electric Operations |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Customer revenues | [1] | 354.4 | 408.3
Other revenues |  | 22.9 | 22.5
Total Operating Revenues |  | 377.3 | 430.8
Corporate and Other |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Customer revenues | [1] | 0.2 | 0.2
Other revenues |  | 0.0 | 0.0
Total Operating Revenues |  | 0.2 | 0.2
Residential |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Customer revenues | [1] | 915.7 | 1,094.1
Residential | Gas Distribution Operations |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Customer revenues | [1] | 796.5 | 975.3
Residential | Electric Operations |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Customer revenues | [1] | 119.2 | 118.8
Residential | Corporate and Other |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Customer revenues | [1] | 0.0 | 0.0
Commercial |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Customer revenues | [1] | 389.6 | 449.8
Commercial | Gas Distribution Operations |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Customer revenues | [1] | 269.4 | 330.5
Commercial | Electric Operations |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Customer revenues | [1] | 120.2 | 119.3
Commercial | Corporate and Other |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Customer revenues | [1] | 0.0 | 0.0
Industrial |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Customer revenues | [1] | 183.3 | 246.2
Industrial | Gas Distribution Operations |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Customer revenues | [1] | 74.2 | 82.9
Industrial | Electric Operations |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Customer revenues | [1] | 109.1 | 163.3
Industrial | Corporate and Other |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Customer revenues | [1] | 0.0 | 0.0
Off-system |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Customer revenues | [1] | 18.7 | 20.1
Off-system | Gas Distribution Operations |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Customer revenues | [1] | 18.7 | 20.1
Off-system | Electric Operations |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Customer revenues | [1] | 0.0 | 0.0
Off-system | Corporate and Other |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Customer revenues | [1] | 0.0 | 0.0
Miscellaneous |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Customer revenues | [1] | 18.6 | 24.3
Miscellaneous | Gas Distribution Operations |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Customer revenues | [1] | 12.5 | 17.2
Miscellaneous | Electric Operations |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Customer revenues | [1] | 5.9 | 6.9
Miscellaneous | Corporate and Other |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Customer revenues | [1] | $ 0.2 | $ 0.2
[1] | Customer revenue amounts exclude intersegment revenues. See Note 21, "Business Segment Information," for discussion of intersegment revenues.

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