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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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The net result for the period of deducting operating expenses from operating revenues.

+ References

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Amount of revenue recognized from goods sold, services rendered, insurance premiums, or other activities that constitute an earning process. Includes, but is not limited to, investment and interest income before deduction of interest expense when recognized as a component of revenue, and sales and trading gain (loss).

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 225
-SubTopic 10
-Section S99
-Paragraph 2
-Subparagraph (SX 210.5-03.1)
-URI http://asc.fasb.org/extlink&oid=63488584&loc=d3e20235-122688

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