Segments (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended				9 Months Ended
	Sep. 30, 2014		Sep. 30, 2013		Sep. 30, 2014 segment		Sep. 30, 2013		Dec. 31, 2013
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	$ 606		$ 450		$ 1,142		$ 1,167
Assets
Total Assets	38,983				38,983				40,411
External [Member]
Revenue
Total Revenue	4,441		3,996		13,014		12,091
Adjusted PTC
Adjusted Pretax Contribution	354	[1]	387	[1]	937	[1]	946	[1]
Reconciliation To Income From Continuing Operations Before Taxes
Unrealized derivative gains (losses)	(11)		7		21		46
Unrealized foreign currency gains (losses)	(62)		21		(95)		(28)
Disposition/acquisition gains	367		4		366		30
Impairment losses	(30)		(189)		(295)		(237)
Loss on extinguishment of debt	(66)		0		(213)		(207)
Pretax contribution	552		230		721		550
Add: income from continuing operations before taxes, attributable to noncontrolling interests	48		235		460		638
Less: Net equity in earnings of affiliates	(6)		15		39		21
INCOME FROM CONTINUING OPERATIONS BEFORE TAXES AND EQUITY IN EARNINGS OF AFFILIATES	606		450		1,142		1,167
Operating Segments [Member]
Revenue
Total Revenue	4,447		3,999		13,027		12,097
Adjusted PTC
Adjusted Pretax Contribution	354	[1]	387	[1]	937	[1]	946	[1]
Intersegment Eliminations [Member]
Revenue
Total Revenue	(6)		(3)		(13)		(6)
Adjusted PTC
Adjusted Pretax Contribution	0	[1]	0	[1]	0	[1]	0	[1]
US - Generation [Member]
Assets
Total Assets	9,899				9,899				9,952
US - Generation [Member] | External [Member]
Revenue
Total Revenue	1,002		966		2,896		2,710
Adjusted PTC
Adjusted Pretax Contribution	159	[1]	135	[1]	320	[1]	336	[1]
US - Generation [Member] | Operating Segments [Member]
Revenue
Total Revenue	1,002		966		2,896		2,710
Adjusted PTC
Adjusted Pretax Contribution	156	[1]	132	[1]	311	[1]	328	[1]
US - Generation [Member] | Intersegment Eliminations [Member]
Revenue
Total Revenue	0		0		0		0
Adjusted PTC
Adjusted Pretax Contribution	3	[1]	3	[1]	9	[1]	8	[1]
Andes - Generation [Member]
Assets
Total Assets	7,641				7,641				7,356
Andes - Generation [Member] | External [Member]
Revenue
Total Revenue	703		628		2,046		2,043
Adjusted PTC
Adjusted Pretax Contribution	119	[1]	115	[1]	280	[1]	291	[1]
Andes - Generation [Member] | Operating Segments [Member]
Revenue
Total Revenue	704		629		2,048		2,044
Adjusted PTC
Adjusted Pretax Contribution	120	[1]	109	[1]	277	[1]	278	[1]
Andes - Generation [Member] | Intersegment Eliminations [Member]
Revenue
Total Revenue	(1)		(1)		(2)		(1)
Adjusted PTC
Adjusted Pretax Contribution	(1)	[1]	6	[1]	3	[1]	13	[1]
Brazil - Generation [Member]
Assets
Total Assets	8,709				8,709				8,388
Brazil - Generation [Member] | External [Member]
Revenue
Total Revenue	1,548		1,275		4,526		3,934
Adjusted PTC
Adjusted Pretax Contribution	1	[1]	85	[1]	186	[1]	206	[1]
Brazil - Generation [Member] | Operating Segments [Member]
Revenue
Total Revenue	1,548		1,275		4,526		3,934
Adjusted PTC
Adjusted Pretax Contribution	0	[1]	84	[1]	184	[1]	204	[1]
Brazil - Generation [Member] | Intersegment Eliminations [Member]
Revenue
Total Revenue	0		0		0		0
Adjusted PTC
Adjusted Pretax Contribution	1	[1]	1	[1]	2	[1]	2	[1]
MCAC - Generation [Member]
Assets
Total Assets	5,115				5,115				5,075
MCAC - Generation [Member] | External [Member]
Revenue
Total Revenue	692		683		2,021		2,046
Adjusted PTC
Adjusted Pretax Contribution	128	[1]	100	[1]	302	[1]	267	[1]
MCAC - Generation [Member] | Operating Segments [Member]
Revenue
Total Revenue	693		683		2,023		2,046
Adjusted PTC
Adjusted Pretax Contribution	124	[1]	96	[1]	284	[1]	256	[1]
MCAC - Generation [Member] | Intersegment Eliminations [Member]
Revenue
Total Revenue	(1)		0		(2)		0
Adjusted PTC
Adjusted Pretax Contribution	4	[1]	4	[1]	18	[1]	11	[1]
EMEA - Generation [Member]
Assets
Total Assets	3,720				3,720				4,191
EMEA - Generation [Member] | External [Member]
Revenue
Total Revenue	371		332		1,067		970
Adjusted PTC
Adjusted Pretax Contribution	82	[1]	69	[1]	276	[1]	242	[1]
EMEA - Generation [Member] | Operating Segments [Member]
Revenue
Total Revenue	371		332		1,067		970
Adjusted PTC
Adjusted Pretax Contribution	79	[1]	66	[1]	267	[1]	234	[1]
EMEA - Generation [Member] | Intersegment Eliminations [Member]
Revenue
Total Revenue	0		0		0		0
Adjusted PTC
Adjusted Pretax Contribution	3	[1]	3	[1]	9	[1]	8	[1]
Asia - Generation [Member]
Assets
Total Assets	3,075				3,075				2,810
Asia - Generation [Member] | External [Member]
Revenue
Total Revenue	125		113		456		388
Adjusted PTC
Adjusted Pretax Contribution	2	[1]	31	[1]	34	[1]	103	[1]
Asia - Generation [Member] | Operating Segments [Member]
Revenue
Total Revenue	125		113		456		388
Adjusted PTC
Adjusted Pretax Contribution	2	[1]	30	[1]	33	[1]	101	[1]
Asia - Generation [Member] | Intersegment Eliminations [Member]
Revenue
Total Revenue	0		0		0		0
Adjusted PTC
Adjusted Pretax Contribution	0	[1]	1	[1]	1	[1]	2	[1]
Corporate Other And Other Eliminations [Member]
Assets
Total Assets	824				824				921
Corporate Other And Other Eliminations [Member] | External [Member]
Revenue
Total Revenue	0		(1)		2		0
Adjusted PTC
Adjusted Pretax Contribution	(137)	[1]	(148)	[1]	(461)	[1]	(499)	[1]
Corporate Other And Other Eliminations [Member] | Operating Segments [Member]
Revenue
Total Revenue	4		1		11		5
Adjusted PTC
Adjusted Pretax Contribution	(127)	[1]	(130)	[1]	(419)	[1]	(455)	[1]
Corporate Other And Other Eliminations [Member] | Intersegment Eliminations [Member]
Revenue
Total Revenue	(4)		(2)		(9)		(5)
Adjusted PTC
Adjusted Pretax Contribution	(10)	[1]	(18)	[1]	(42)	[1]	(44)	[1]
Discontinued Operations [Member]
Assets
Total Assets	$ 0				$ 0				$ 1,718

[1] Adjusted pretax contribution 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.