Business Segments (Schedule of Revenue, By Products and Services) (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Segment Reporting Information [Line Items]
Revenues	$ 5,799	$ 6,482	$ 5,555	$ 5,729	$ 5,577	$ 6,576	$ 5,213	$ 5,377	$ 23,565	$ 22,743	$ 22,371
Electric Utilities and Infrastructure [Member]
Segment Reporting Information [Line Items]
Revenues									21,300	21,336	21,489
Gas Utilities and Infrastructure [Member]
Segment Reporting Information [Line Items]
Revenues									1,743	875	536
Commercial Renewables [Member]
Segment Reporting Information [Line Items]
Revenues									460	484	286
Total Reportable Segments [Member]
Segment Reporting Information [Line Items]
Revenues									23,503	22,695	22,311
Retail Electric [Member]
Segment Reporting Information [Line Items]
Revenues									18,177	18,338	18,695
Retail Electric [Member] | Electric Utilities and Infrastructure [Member]
Segment Reporting Information [Line Items]
Revenues									18,177	18,338	18,695
Wholesale Electric [Member]
Segment Reporting Information [Line Items]
Revenues									2,479	2,398	2,259
Wholesale Electric [Member] | Electric Utilities and Infrastructure [Member]
Segment Reporting Information [Line Items]
Revenues									2,104	2,095	2,014
Wholesale Electric [Member] | Commercial Renewables [Member]
Segment Reporting Information [Line Items]
Revenues									375	303	245
Retail Natural Gas [Member]
Segment Reporting Information [Line Items]
Revenues									1,732	871	546
Retail Natural Gas [Member] | Gas Utilities and Infrastructure [Member]
Segment Reporting Information [Line Items]
Revenues									1,732	871	546
Other Revenues [Member]
Segment Reporting Information [Line Items]
Revenues									1,239	1,144	848
Other Revenues [Member] | Electric Utilities and Infrastructure [Member]
Segment Reporting Information [Line Items]
Revenues									1,050	933	812
Other Revenues [Member] | Gas Utilities and Infrastructure [Member]
Segment Reporting Information [Line Items]
Revenues									104	30	(5)
Other Revenues [Member] | Commercial Renewables [Member]
Segment Reporting Information [Line Items]
Revenues									85	181	41
Operating Segments [Member] | Electric Utilities and Infrastructure [Member]
Segment Reporting Information [Line Items]
Revenues									21,331	21,366	21,521
Operating Segments [Member] | Gas Utilities and Infrastructure [Member]
Segment Reporting Information [Line Items]
Revenues									1,836	901	541
Operating Segments [Member] | Commercial Renewables [Member]
Segment Reporting Information [Line Items]
Revenues									460	484	286
Operating Segments [Member] | Total Reportable Segments [Member]
Segment Reporting Information [Line Items]
Revenues									$ 23,627	$ 22,751	$ 22,348