Segments (Details) $ in Millions		3 Months Ended				6 Months Ended
		Jun. 30, 2016 USD ($)		Jun. 30, 2015 USD ($)		Jun. 30, 2016 USD ($) segment	Jun. 30, 2015 USD ($)	Dec. 31, 2015 USD ($)
Segment Reporting Information [Line Items]
Number of strategic business units | segment						6
Number of reportable segments | segment						6
Reconciliation To Income From Continuing Operations Before Taxes
Income (Loss) from Equity Method Investments		$ (7)		$ (1)		$ (14)	$ (15)
INCOME (LOSS) FROM CONTINUING OPERATIONS BEFORE TAXES AND EQUITY IN EARNINGS OF AFFILIATES		(22)		396		151	743
Assets
Total Assets		36,974				36,974		$ 36,470
External [Member]
Reconciliation To Income From Continuing Operations Before Taxes
Unrealized derivative gains (losses)		(30)		2		4	17
Unrealized foreign currency gains (losses)		(17)		4		(9)	(43)
Disposition/acquisition gains		(17)		4		2	9
Impairment losses		(235)		(30)		(285)	(36)
Loss on extinguishment of debt		(6)		(112)		(6)	(138)
Pretax contribution		(145)		128		51	331
Add: income from continuing operations before taxes, attributable to noncontrolling interests		130		269		114	427
INCOME (LOSS) FROM CONTINUING OPERATIONS BEFORE TAXES AND EQUITY IN EARNINGS OF AFFILIATES		(22)		396		151	743
Operating Segments [Member]
Revenue
Total Revenue		3,229		3,656		6,500	7,414
Adjusted PTC
Adjusted Pretax Contribution	[1]	160		260		345	522
Intersegment Eliminations [Member]
Revenue
Total Revenue		(6)		(11)		(11)	(17)
UNITED STATES
Assets
Total Assets		9,705				9,705		9,800
UNITED STATES | Operating Segments [Member]
Revenue
Total Revenue		811		831		1,666	1,828
Adjusted PTC
Adjusted Pretax Contribution		58	[1]	56	[1]	143	162
Andes - Generation [Member]
Assets
Total Assets		8,755				8,755		8,594
Andes - Generation [Member] | Operating Segments [Member]
Revenue
Total Revenue		575		630		1,197	1,242
Adjusted PTC
Adjusted Pretax Contribution		84	[1]	81	[1]	145	172
BRAZIL
Assets
Total Assets		6,085				6,085		5,209
BRAZIL | Operating Segments [Member]
Revenue
Total Revenue		895		1,113		1,734	2,217
Adjusted PTC
Adjusted Pretax Contribution		7	[1]	51	[1]	12	82
MCAC - Generation [Member]
Assets
Total Assets		5,146				5,146		4,820
MCAC - Generation [Member] | Operating Segments [Member]
Revenue
Total Revenue		530		601		1,049	1,199
Adjusted PTC
Adjusted Pretax Contribution		75	[1]	106	[1]	123	156
Europe [Member]
Assets
Total Assets		2,807				2,807		3,101
Europe [Member] | Operating Segments [Member]
Revenue
Total Revenue		222		299		468	629
Adjusted PTC
Adjusted Pretax Contribution		34	[1]	41	[1]	103	126
Asia [Member]
Assets
Total Assets		3,126				3,126		3,099
Asia [Member] | Operating Segments [Member]
Revenue
Total Revenue		201		187		395	306
Adjusted PTC
Adjusted Pretax Contribution		26	[1]	30	[1]	48	42
Corporate Other And Other Eliminations [Member]
Assets
Total Assets		302				302		541
Corporate Other And Other Eliminations [Member] | Operating Segments [Member]
Revenue
Total Revenue		1		6		2	10
Adjusted PTC
Adjusted Pretax Contribution		(124)	[1]	$ (105)	[1]	(229)	$ (218)
Discontinued Operations [Member]
Assets
Total Assets		$ 1,048				$ 1,048		$ 1,306

[1] Total AssetsJune 30, 2016 December 31, 2015US SBU$9,705 $9,800Andes SBU8,755 8,594Brazil SBU6,085 5,209MCAC SBU5,146 4,820Europe SBU2,807 3,101Asia SBU3,126 3,099Assets of discontinued operations and held-for-sale businesses1,048 1,306Corporate and Other302 541Total Assets$36,974 $36,470