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Segments Of Business (Schedule Of Operating Income Derived From Revenues And Expenses By Segment) (Details) - USD ($) $ in Millions		3 Months Ended								12 Months Ended
		Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Segment Reporting Information [Line Items]
Operating Revenues										$ 5,114.5	$ 4,874.6	$ 4,492.5
Operating Income (Loss)		$ (78.4)	$ (315.9)	$ 118.4	$ 400.6	$ 270.6	$ 111.2	$ 124.0	$ 415.4	124.7	921.2	866.1
Consolidated Depreciation and Amortization										599.6	570.3	547.1
Consolidated Assets		21,804.0				19,961.7				21,804.0	19,961.7	18,691.9
Payments to Acquire Property Plant and Equipment Including Captial Expenditures From Current Liabilities And Equity Method Investments	[1]									1,814.6	1,753.8	1,490.4
Gas Distribution Operations
Segment Reporting Information [Line Items]
Operating Revenues										3,406.4
Intersegment										3,419.5	3,102.1	2,830.6
Operating Income (Loss)										(254.1)	550.1	569.7
Consolidated Depreciation and Amortization										301.0	269.3	252.9
Consolidated Assets		13,527.0				12,048.8				13,527.0	12,048.8	11,096.4
Payments to Acquire Property Plant and Equipment Including Captial Expenditures From Current Liabilities And Equity Method Investments	[1]									1,315.3	1,125.6	1,054.4
Electric Operations
Segment Reporting Information [Line Items]
Operating Revenues										1,707.4
Intersegment										1,708.2	1,786.5	1,661.6
Operating Income (Loss)										386.1	367.4	301.3
Consolidated Depreciation and Amortization										262.9	277.8	274.5
Consolidated Assets		5,735.2				5,478.6				5,735.2	5,478.6	5,233.3
Payments to Acquire Property Plant and Equipment Including Captial Expenditures From Current Liabilities And Equity Method Investments	[1]									499.3	592.4	420.6
Corporate and Other
Segment Reporting Information [Line Items]
Operating Revenues										0.7
Intersegment										518.3	511.8	426.8
Operating Income (Loss)										(7.3)	3.7	(4.9)
Consolidated Depreciation and Amortization										35.7	23.2	19.7
Consolidated Assets		$ 2,541.8				$ 2,434.3				2,541.8	2,434.3	2,362.2
Payments to Acquire Property Plant and Equipment Including Captial Expenditures From Current Liabilities And Equity Method Investments	[1]									0.0	35.8	15.4
Eliminations
Segment Reporting Information [Line Items]
Intersegment										(531.5)	(525.8)	(426.5)
Unaffiliated | Gas Distribution Operations
Segment Reporting Information [Line Items]
Operating Revenues										3,406.4	3,087.9	2,818.2
Unaffiliated | Electric Operations
Segment Reporting Information [Line Items]
Operating Revenues										1,707.4	1,785.7	1,660.8
Unaffiliated | Corporate and Other
Segment Reporting Information [Line Items]
Operating Revenues										0.7	1.0	13.5
Intersegment | Gas Distribution Operations
Segment Reporting Information [Line Items]
Intersegment										13.1	14.2	12.4
Intersegment | Electric Operations
Segment Reporting Information [Line Items]
Intersegment										0.8	0.8	0.8
Intersegment | Corporate and Other
Segment Reporting Information [Line Items]
Intersegment										$ 517.6	$ 510.8	$ 413.3
[1] Amounts differ from those presented on the Statements of Consolidated Cash Flows primarily due to the inclusion of capital expenditures included in current liabilities and AFUDC Equity.

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