Acquisitions and Dispositions (International Energy Discontinued Operations) (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
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Income tax expense (benefit)									$ (30)	$ 89	$ 149
Income (Loss) From Discontinued Operations, net of tax	$ (598)	$ 180	$ (112)	$ 122	$ 49	$ 45	$ (29)	$ 112	(408)	177	(649)
Asset Impairment Charges									18	106	81
International Energy [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Asset Impairment Charges									194
Cumulative foreign currency translation losses									620
Income (Loss) from Discontinued Operation, before Income Tax, Attributable to Parent									(445)	221	360
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]
Foreign Income Tax Expense (Benefit), Continuing Operations									(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)		373
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	1,417
Fuel used in electric generation and purchased power									227	306	486
Cost of natural gas									43	53	63
Operation, maintenance and other									341	334	352
Depreciation and amortization									62	92	97
Property and other taxes									15	7	9
Impairment charges									194	13
(Loss) Gains on Sales of Other Assets and Other, net									(3)	6	6
Other income and expenses, net									58	23	47
Interest Expense									82	85	93
Pretax loss on disposal									(514)
(Loss) Income before income taxes									(435)	227	370
Income tax expense (benefit)									99	70	443
Income (Loss) From Discontinued Operations, net of tax									$ (534)	$ 157	$ (73)