Segments (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2015 segment		Mar. 31, 2014		Dec. 31, 2014
Segment Reporting Information [Line Items]
Number of strategic business units	6
Number of reportable segments	6
Reconciliation To Income From Continuing Operations Before Taxes
INCOME FROM CONTINUING OPERATIONS BEFORE TAXES AND EQUITY IN EARNINGS OF AFFILIATES	$ 335		$ 118
Assets
Total Assets	37,997				38,966
External [Member]
Revenue
Total Revenue	3,984		4,262
Adjusted PTC
Adjusted Pretax Contribution	252	[1]	243	[1]
Reconciliation To Income From Continuing Operations Before Taxes
Unrealized derivative gains (losses)	15		10
Unrealized foreign currency gains (losses)	(47)		(26)
Disposition/acquisition gains	5		1
Impairment losses	(6)		(166)
Loss on extinguishment of debt	(27)		(134)
Pretax contribution	192		(72)
Add: income from continuing operations before taxes, attributable to noncontrolling interests	158		215
Less: Net equity in earnings of affiliates	15		25
INCOME FROM CONTINUING OPERATIONS BEFORE TAXES AND EQUITY IN EARNINGS OF AFFILIATES	335		118
Operating Segments [Member]
Revenue
Total Revenue	3,990		4,265
Adjusted PTC
Adjusted Pretax Contribution	252	[1]	243	[1]
Intersegment Eliminations [Member]
Revenue
Total Revenue	(6)		(3)
Adjusted PTC
Adjusted Pretax Contribution	0	[1]	0	[1]
US - Generation [Member]
Assets
Total Assets	9,874				10,062
US - Generation [Member] | External [Member]
Revenue
Total Revenue	997		1,001
Adjusted PTC
Adjusted Pretax Contribution	109	[1]	78	[1]
US - Generation [Member] | Operating Segments [Member]
Revenue
Total Revenue	997		1,001
Adjusted PTC
Adjusted Pretax Contribution	106	[1]	75	[1]
US - Generation [Member] | Intersegment Eliminations [Member]
Revenue
Total Revenue	0		0
Adjusted PTC
Adjusted Pretax Contribution	3	[1]	3	[1]
Andes - Generation [Member]
Assets
Total Assets	8,304				7,888
Andes - Generation [Member] | External [Member]
Revenue
Total Revenue	610		620
Adjusted PTC
Adjusted Pretax Contribution	94	[1]	56	[1]
Andes - Generation [Member] | Operating Segments [Member]
Revenue
Total Revenue	612		620
Adjusted PTC
Adjusted Pretax Contribution	91	[1]	53	[1]
Andes - Generation [Member] | Intersegment Eliminations [Member]
Revenue
Total Revenue	(2)		0
Adjusted PTC
Adjusted Pretax Contribution	3	[1]	3	[1]
Brazil - Generation [Member]
Assets
Total Assets	7,456				8,439
Brazil - Generation [Member] | External [Member]
Revenue
Total Revenue	1,330		1,445
Adjusted PTC
Adjusted Pretax Contribution	22	[1]	70	[1]
Brazil - Generation [Member] | Operating Segments [Member]
Revenue
Total Revenue	1,330		1,445
Adjusted PTC
Adjusted Pretax Contribution	21	[1]	69	[1]
Brazil - Generation [Member] | Intersegment Eliminations [Member]
Revenue
Total Revenue	0		0
Adjusted PTC
Adjusted Pretax Contribution	1	[1]	1	[1]
MCAC - Generation [Member]
Assets
Total Assets	5,013				4,948
MCAC - Generation [Member] | External [Member]
Revenue
Total Revenue	597		637
Adjusted PTC
Adjusted Pretax Contribution	54	[1]	69	[1]
MCAC - Generation [Member] | Operating Segments [Member]
Revenue
Total Revenue	598		638
Adjusted PTC
Adjusted Pretax Contribution	50	[1]	65	[1]
MCAC - Generation [Member] | Intersegment Eliminations [Member]
Revenue
Total Revenue	(1)		(1)
Adjusted PTC
Adjusted Pretax Contribution	4	[1]	4	[1]
EMEA - Generation [Member]
Assets
Total Assets	3,313				3,525
EMEA - Generation [Member] | External [Member]
Revenue
Total Revenue	330		391
Adjusted PTC
Adjusted Pretax Contribution	88	[1]	118	[1]
EMEA - Generation [Member] | Operating Segments [Member]
Revenue
Total Revenue	330		391
Adjusted PTC
Adjusted Pretax Contribution	85	[1]	115	[1]
EMEA - Generation [Member] | Intersegment Eliminations [Member]
Revenue
Total Revenue	0		0
Adjusted PTC
Adjusted Pretax Contribution	3	[1]	3	[1]
Asia - Generation [Member]
Assets
Total Assets	3,009				2,972
Asia - Generation [Member] | External [Member]
Revenue
Total Revenue	119		168
Adjusted PTC
Adjusted Pretax Contribution	12	[1]	9	[1]
Asia - Generation [Member] | Operating Segments [Member]
Revenue
Total Revenue	119		168
Adjusted PTC
Adjusted Pretax Contribution	12	[1]	8	[1]
Asia - Generation [Member] | Intersegment Eliminations [Member]
Revenue
Total Revenue	0		0
Adjusted PTC
Adjusted Pretax Contribution	0	[1]	1	[1]
Corporate Other And Other Eliminations [Member]
Assets
Total Assets	849				1,132
Corporate Other And Other Eliminations [Member] | External [Member]
Revenue
Total Revenue	1		0
Adjusted PTC
Adjusted Pretax Contribution	(127)	[1]	(157)	[1]
Corporate Other And Other Eliminations [Member] | Operating Segments [Member]
Revenue
Total Revenue	4		2
Adjusted PTC
Adjusted Pretax Contribution	(113)	[1]	(142)	[1]
Corporate Other And Other Eliminations [Member] | Intersegment Eliminations [Member]
Revenue
Total Revenue	(3)		(2)
Adjusted PTC
Adjusted Pretax Contribution	(14)	[1]	(15)	[1]
Discontinued Operations [Member]
Assets
Total Assets	$ 179				$ 0

[1] Adjusted PTC in each segment before intersegment eliminations includes the effect of intercompany transactions with other segments except for interest, charges for certain management fees and the write-off of intercompany balances.