Acquisitions and Dispositions (International Energy Discontinued Operations) (Details) - USD ($) $ in Millions	3 Months Ended							12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Income tax expense (benefit)								$ (6)	$ (30)	$ 89
Income (Loss) From Discontinued Operations, net of tax	$ (2)	$ (2)	$ (2)	$ (598)	$ 180	$ (112)	$ 122	(6)	(408)	177
Asset Impairment Charges								$ 282	18	106
International Energy [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Income (Loss) From Discontinued Operations, net of tax									(534)	157
Asset Impairment Charges									194
Cumulative foreign currency translation losses									620
Income (Loss) from Discontinued Operation, before Income Tax, Attributable to Parent									(445)	221
Income tax expense on disposal									126
After-tax loss on disposal									640
Previously Remitted Earnings [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Income tax expense (benefit)									(95)
Previously Remitted Earnings [Member] | International Energy [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Foreign Income Tax Expense (Benefit), Continuing Operations									(95)
Discontinued Operations, Disposed of by Sale [Member] | International Energy [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Operating Revenues									988	1,088
Fuel used in electric generation and purchased power									227	306
Cost of natural gas									43	53
Operation, maintenance and other									341	334
Depreciation and amortization									62	92
Property and other taxes									15	7
Impairment charges									194	13
(Loss) Gains on Sales of Other Assets and Other, net									(3)	6
Other income and expenses, net									58	23
Interest Expense									82	85
Pretax loss on disposal									514
(Loss) Income before income taxes									(435)	227
Income tax expense (benefit)									$ 99	$ 70