Acquisitions and Dispositions (Discontinued Operations) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Income From Discontinued Operations, net of tax	$ (2)	$ (112)	$ (2)	$ 10
International Energy [Member] | Discontinued Operations, Disposed of by Sale [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Operating Revenues		270		516
Fuel used in electric generation and purchased power		70		117
Cost of natural gas		12		23
Operation, maintenance and other		84		155
Deprecation and amortization		22		44
Property and other taxes		2		5
Impairment Charges		194		194
Gains on Sales of Other Assets and Other, net		1		1
Other Income and Expenses, net		11		21
Interest Expense		22		44
Income before income taxes		(124)		(44)
Income tax benefit		(13)		(52)
Income From Discontinued Operations, net of tax		(111)		8
Other Disposal Groups [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Income From Discontinued Operations, net of tax		$ (1)		2
Previously Remitted Earnings [Member] | International Energy [Member] | Discontinued Operations, Disposed of by Sale [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Income tax benefit				$ (95)