Business Segments (Schedule of Revenue, By Products and Services) (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Segment Reporting Information [Line Items]
Operating revenues	$ 5,577	$ 6,576	$ 5,213	$ 5,377	$ 5,075	$ 6,202	$ 5,302	$ 5,792	$ 22,743	$ 22,371	$ 22,509
Electric Utilities and Infrastructure [Member]
Segment Reporting Information [Line Items]
Operating revenues									21,336	21,489	21,655
Gas Utilities and Infrastructure [Member]
Segment Reporting Information [Line Items]
Operating revenues									875	536	573
Commercial Renewables [Member]
Segment Reporting Information [Line Items]
Operating revenues									484	286	235
Total Reportable Segments [Member]
Segment Reporting Information [Line Items]
Operating revenues									22,695	22,311	22,463
Retail Electric [Member]
Segment Reporting Information [Line Items]
Operating revenues									18,338	18,695	19,007
Retail Electric [Member] | Electric Utilities and Infrastructure [Member]
Segment Reporting Information [Line Items]
Operating revenues									18,338	18,695	19,007
Wholesale Electric [Member]
Segment Reporting Information [Line Items]
Operating revenues									2,398	2,259	2,115
Wholesale Electric [Member] | Electric Utilities and Infrastructure [Member]
Segment Reporting Information [Line Items]
Operating revenues									2,095	2,014	1,879
Wholesale Electric [Member] | Commercial Renewables [Member]
Segment Reporting Information [Line Items]
Operating revenues									303	245	236
Retail Natural Gas [Member]
Segment Reporting Information [Line Items]
Operating revenues									871	546	571
Retail Natural Gas [Member] | Gas Utilities and Infrastructure [Member]
Segment Reporting Information [Line Items]
Operating revenues									871	546	571
Other Revenues [Member]
Segment Reporting Information [Line Items]
Operating revenues									1,144	848	812
Other Revenues [Member] | Electric Utilities and Infrastructure [Member]
Segment Reporting Information [Line Items]
Operating revenues									933	812	805
Other Revenues [Member] | Gas Utilities and Infrastructure [Member]
Segment Reporting Information [Line Items]
Operating revenues									30	(5)	7
Other Revenues [Member] | Commercial Renewables [Member]
Segment Reporting Information [Line Items]
Operating revenues									181	41
Operating Segments [Member] | Electric Utilities and Infrastructure [Member]
Segment Reporting Information [Line Items]
Operating revenues									21,366	21,521	21,691
Operating Segments [Member] | Gas Utilities and Infrastructure [Member]
Segment Reporting Information [Line Items]
Operating revenues									901	541	578
Operating Segments [Member] | Commercial Renewables [Member]
Segment Reporting Information [Line Items]
Operating revenues									484	286	236
Operating Segments [Member] | Total Reportable Segments [Member]
Segment Reporting Information [Line Items]
Operating revenues									$ 22,751	$ 22,348	$ 22,505