Segments and Geographic Information Segment and Geographic Information (Revenue and Assets by Country) (Details) - USD ($) $ in Millions		3 Months Ended								12 Months Ended
		Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenue		$ 2,643	$ 2,693	$ 2,613	$ 2,581	$ 2,660	$ 2,639	$ 2,452	$ 2,530	$ 10,530	$ 10,281	$ 11,260
Property, plant and equipment, net		20,296				20,415				20,296	20,415
US SBU
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenue										3,240	3,489	3,597
Property, plant and equipment, net		7,403				7,397				7,403	7,397
Total Non-U.S.
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenue										7,290	6,792	7,663
Property, plant and equipment, net		12,893				13,018				12,893	13,018
Brazil
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenue										541	450	962
Property, plant and equipment, net		1,286				789				1,286	789
CHILE
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenue										1,944	1,707	1,523
Property, plant and equipment, net		5,066				4,995				5,066	4,995
Dominican Republic
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenue										826	614	632
Property, plant and equipment, net		935				914				935	914
El Salvador
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenue										686	601	736
Property, plant and equipment, net		340				327				340	327
Colombia
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenue										332	437	557
Property, plant and equipment, net		332				451				332	451
PHILIPPINES
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenue										449	401	406
Property, plant and equipment, net		0				866				0	866
ARGENTINA
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenue										435	359	399
Property, plant and equipment, net		223				195				223	195
Mexico
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenue										352	342	383
Property, plant and equipment, net		687				699				687	699
Vietnam
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenue										278	340	233
Property, plant and equipment, net	[1]	2				1				2	1
United Kingdom
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenue										328	337	396
Property, plant and equipment, net		108				151				108	151
BULGARIA
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenue										367	334	382
Property, plant and equipment, net		1,290				1,174				1,290	1,174
Panama
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenue										338	312	297
Property, plant and equipment, net		1,615				1,233				1,615	1,233
Puerto Rico
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenue										247	301	302
Property, plant and equipment, net		565				583				565	583
JORDAN
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenue										95	136	248
Property, plant and equipment, net		431				452				431	452
KAZAKHSTAN
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenue										67	103	155
Property, plant and equipment, net		0				178				0	178
Other Non-U.S.
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenue										5	18	$ 52
Property, plant and equipment, net		$ 13				$ 10				$ 13	$ 10

[1] The Mong Duong II power project is accounted for as a service concession arrangement. Costs of construction of the plant have been deferred in Service concession assets on the Consolidated Balance Sheets.