Dispositions Dispositions (Details) - USD ($) $ in Millions					3 Months Ended				9 Months Ended
	Oct. 02, 2017	Apr. 07, 2017	Jan. 27, 2016	Jan. 01, 2016	Sep. 30, 2017	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Sep. 30, 2017	Sep. 30, 2016
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Impairment of Long-Lived Assets Held-for-use					$ 2	$ 79			$ 260	$ 473
Assets Carrying Amount Disclosure Nonrecurring					622				622
Proceeds from the sale of businesses, net of cash sold, and equity method investments									39	157
Gain (Loss) on Disposition of Business					1	0			49	(30)
Proceeds from sale of ownership interest									0	(134)
Disposal Group, Disposed of by Sale, Not Discontinued Operations [Member] | Kazakhstan [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Proceeds from the sale of businesses, net of cash sold, and equity method investments		$ 24
Gain (Loss) on Disposition of Business		$ 49
Pre-tax income of disposed businesses, Excluding gain on disposal, included in continuing operations					0	(2)			13	5
Disposal Group, Held-for-sale, Not Discontinued Operations [Member] | Kazakhstan Hydro [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Pre-tax income of disposed businesses, Excluding gain on disposal, included in continuing operations					12	10			33	28
UK Wind Projects [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Gain (Loss) on Disposition of Business							$ 20
Kazakhstan [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Impairment of Long-Lived Assets to be Disposed of					$ 0	0			$ 94	$ 0
DPLER [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Proceeds from the sale of businesses, net of cash sold, and equity method investments				$ 76
Gain (Loss) on Disposition of Business				$ (49)
Kelanitissa [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Proceeds from the sale of businesses, net of cash sold, and equity method investments			$ 18
Gain (Loss) on Disposition of Business			$ 5
Subsequent Event [Member] | Disposal Group, Held-for-sale, Not Discontinued Operations [Member] | Kazakhstan Hydro [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Gain (Loss) on Disposition of Business	$ (37)
Disposal Group Not Discontinued Operation Ownership Interest Sold	100.00%
Parent Company [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Impairment of Long-Lived Assets Held-for-use						$ 23		$ 49