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Business Segment Information (Schedule Of Operating Income Derived From Revenues And Expenses By Segment) (Details) - USD ($) $ in Millions | 3 Months Ended
--- | ---
Mar. 31, 2017 | Mar. 31, 2016
Segment Reporting Information [Line Items] |  |
Revenues | $ 1,598.6 | $ 1,436.6
Consolidated Operating Income (Loss) | 416.5 | 381.4
Gas Distribution Operations |  |
Segment Reporting Information [Line Items] |  |
Revenues | 1,179.8 | 1,044.0
Consolidated Operating Income (Loss) | 340.7 | 314.9
Gas Distribution Operations | Unaffiliated |  |
Segment Reporting Information [Line Items] |  |
Revenues | 1,176.3 | 1,040.8
Gas Distribution Operations | Intersegment |  |
Segment Reporting Information [Line Items] |  |
Revenues | 3.5 | 3.2
Electric Operations |  |
Segment Reporting Information [Line Items] |  |
Revenues | 421.9 | 392.3
Consolidated Operating Income (Loss) | 77.0 | 70.3
Electric Operations | Unaffiliated |  |
Segment Reporting Information [Line Items] |  |
Revenues | 421.7 | 392.1
Electric Operations | Intersegment |  |
Segment Reporting Information [Line Items] |  |
Revenues | 0.2 | 0.2
Corporate and Other |  |
Segment Reporting Information [Line Items] |  |
Revenues | 120.2 | 102.5
Consolidated Operating Income (Loss) | (1.2) | (3.8)
Corporate and Other | Unaffiliated |  |
Segment Reporting Information [Line Items] |  |
Revenues | 0.6 | 3.7
Corporate and Other | Intersegment |  |
Segment Reporting Information [Line Items] |  |
Revenues | 119.6 | 98.8
Eliminations |  |
Segment Reporting Information [Line Items] |  |
Revenues | $ (123.3) | $ (102.2)

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