Segments (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended				9 Months Ended				12 Months Ended
	Sep. 30, 2013		Sep. 30, 2012		Sep. 30, 2013 segment		Sep. 30, 2012		Dec. 31, 2012 segment
Segment Reporting Information [Line Items]
Number of strategic business units					6
Number of reportable segments					9				8
Revenue
Total Revenue	$ 4,003		$ 4,355		$ 12,108		$ 12,807
Adjusted PTC
External Adjusted Pre-tax Contribution	387	[1]	380	[1]	946	[1]	1,002	[1]
Reconciliation To Income From Continuing Operations Before Taxes
Unrealized derivative gains (losses)	7		(22)		46		(88)
Unrealized foreign currency gains (losses)	22		22		(25)		8
Disposition/acquisition gains	4		25		30		206
Impairment losses	(236)		(1,893)		(284)		(1,973)
Loss on extinguishment of debt					(207)		0
Pre-tax contribution	184		(1,488)		506		(845)
Add: income from continuing operations before taxes, attributable to noncontrolling interests	217		230		620		586
Less: Net equity in earnings of affiliates	15		25		21		49
INCOME (LOSS) FROM CONTINUING OPERATIONS BEFORE TAXES AND EQUITY IN EARNINGS OF AFFILIATES	386		(1,283)		1,105		(308)
Assets
Total Assets	41,250				41,250				41,830
Intersegment Eliminations [Member]
Revenue
Total Revenue	(223)		(272)		(759)		(823)
Adjusted PTC
External Adjusted Pre-tax Contribution	0	[1]	0	[1]	0	[1]	0	[1]
Operating Segments [Member]
Revenue
Total Revenue	4,226		4,627		12,867		13,630
Adjusted PTC
External Adjusted Pre-tax Contribution	387	[1]	380	[1]	946	[1]	1,002	[1]
US - Generation [Member]
Revenue
Total Revenue	207		222		567		636
Adjusted PTC
External Adjusted Pre-tax Contribution	47	[1]	51	[1]	157	[1]	149	[1]
Assets
Total Assets	3,151				3,151				3,259
US - Generation [Member] | Intersegment Eliminations [Member]
Revenue
Total Revenue	0		0		0		0
Adjusted PTC
External Adjusted Pre-tax Contribution	3	[1]	11	[1]	7	[1]	31	[1]
US - Generation [Member] | Operating Segments [Member]
Revenue
Total Revenue	207		222		567		636
Adjusted PTC
External Adjusted Pre-tax Contribution	44	[1]	40	[1]	150	[1]	118	[1]
US - Utilities [Member]
Revenue
Total Revenue	763		796		2,159		2,206
Adjusted PTC
External Adjusted Pre-tax Contribution	87	[1]	108	[1]	182	[1]	198	[1]
Assets
Total Assets	7,924				7,924				7,534
US - Utilities [Member] | Intersegment Eliminations [Member]
Revenue
Total Revenue	0		0		0		0
Adjusted PTC
External Adjusted Pre-tax Contribution	0	[1]	0	[1]	1	[1]	1	[1]
US - Utilities [Member] | Operating Segments [Member]
Revenue
Total Revenue	763		796		2,159		2,206
Adjusted PTC
External Adjusted Pre-tax Contribution	87	[1]	108	[1]	181	[1]	197	[1]
Andes - Gener - Generation [Member]
Revenue
Total Revenue	539		560		1,738		1,685
Adjusted PTC
External Adjusted Pre-tax Contribution	62	[1]	84	[1]	198	[1]	193	[1]
Assets
Total Assets	5,969				5,969				5,820
Andes - Gener - Generation [Member] | Intersegment Eliminations [Member]
Revenue
Total Revenue	0		(8)		0		(26)
Adjusted PTC
External Adjusted Pre-tax Contribution	3	[1]	(4)	[1]	8	[1]	(14)	[1]
Andes - Gener - Generation [Member] | Operating Segments [Member]
Revenue
Total Revenue	539		568		1,738		1,711
Adjusted PTC
External Adjusted Pre-tax Contribution	59	[1]	88	[1]	190	[1]	207	[1]
Andes - Other - Generation [Member]
Revenue
Total Revenue	89		206		305		567
Adjusted PTC
External Adjusted Pre-tax Contribution	53	[1]	21	[1]	89	[1]	63	[1]
Assets
Total Assets	761				761				799
Andes - Other - Generation [Member] | Intersegment Eliminations [Member]
Revenue
Total Revenue	0		(1)		(1)		(1)
Adjusted PTC
External Adjusted Pre-tax Contribution	3	[1]	1	[1]	5	[1]	2	[1]
Andes - Other - Generation [Member] | Operating Segments [Member]
Revenue
Total Revenue	89		207		306		568
Adjusted PTC
External Adjusted Pre-tax Contribution	50	[1]	20	[1]	84	[1]	61	[1]
Brazil - Generation [Member]
Revenue
Total Revenue	50		8		185		57
Adjusted PTC
External Adjusted Pre-tax Contribution	(16)	[1]	(18)	[1]	(38)	[1]	(48)	[1]
Assets
Total Assets	1,494				1,494				1,590
Brazil - Generation [Member] | Intersegment Eliminations [Member]
Revenue
Total Revenue	(222)		(260)		(752)		(790)
Adjusted PTC
External Adjusted Pre-tax Contribution	(53)	[1]	(63)	[1]	(181)	[1]	(190)	[1]
Brazil - Generation [Member] | Operating Segments [Member]
Revenue
Total Revenue	272		268		937		847
Adjusted PTC
External Adjusted Pre-tax Contribution	37	[1]	45	[1]	143	[1]	142	[1]
Brazil - Utilities [Member]
Revenue
Total Revenue	1,224		1,448		3,749		4,209
Adjusted PTC
External Adjusted Pre-tax Contribution	84	[1]	82	[1]	183	[1]	233	[1]
Assets
Total Assets	7,300				7,300				8,120
Brazil - Utilities [Member] | Intersegment Eliminations [Member]
Revenue
Total Revenue	0		0		0		0
Adjusted PTC
External Adjusted Pre-tax Contribution	36	[1]	42	[1]	122	[1]	128	[1]
Brazil - Utilities [Member] | Operating Segments [Member]
Revenue
Total Revenue	1,224		1,448		3,749		4,209
Adjusted PTC
External Adjusted Pre-tax Contribution	48	[1]	40	[1]	61	[1]	105	[1]
MCAC - Generation [Member]
Revenue
Total Revenue	469		436		1,397		1,254
Adjusted PTC
External Adjusted Pre-tax Contribution	95	[1]	89	[1]	238	[1]	252	[1]
Assets
Total Assets	4,434				4,434				4,293
MCAC - Generation [Member] | Intersegment Eliminations [Member]
Revenue
Total Revenue	0		(1)		(1)		(2)
Adjusted PTC
External Adjusted Pre-tax Contribution	5	[1]	2	[1]	11	[1]	6	[1]
MCAC - Generation [Member] | Operating Segments [Member]
Revenue
Total Revenue	469		437		1,398		1,256
Adjusted PTC
External Adjusted Pre-tax Contribution	90	[1]	87	[1]	227	[1]	246	[1]
EMEA - Generation [Member]
Revenue
Total Revenue	333		268		970		997
Adjusted PTC
External Adjusted Pre-tax Contribution	71	[1]	58	[1]	242	[1]	285	[1]
Assets
Total Assets	4,125				4,125				4,178
EMEA - Generation [Member] | Intersegment Eliminations [Member]
Revenue
Total Revenue	0		0		0		(1)
Adjusted PTC
External Adjusted Pre-tax Contribution	3	[1]	5	[1]	6	[1]	(3)	[1]
EMEA - Generation [Member] | Operating Segments [Member]
Revenue
Total Revenue	333		268		970		998
Adjusted PTC
External Adjusted Pre-tax Contribution	68	[1]	53	[1]	236	[1]	288	[1]
Asia - Generation [Member]
Revenue
Total Revenue	113		191		388		553
Adjusted PTC
External Adjusted Pre-tax Contribution	31	[1]	53	[1]	103	[1]	142	[1]
Assets
Total Assets	2,717				2,717				2,583
Asia - Generation [Member] | Intersegment Eliminations [Member]
Revenue
Total Revenue	0		0		0		0
Adjusted PTC
External Adjusted Pre-tax Contribution	1	[1]	0	[1]	2	[1]	1	[1]
Asia - Generation [Member] | Operating Segments [Member]
Revenue
Total Revenue	113		191		388		553
Adjusted PTC
External Adjusted Pre-tax Contribution	30	[1]	53	[1]	101	[1]	141	[1]
Corporate Other And Other Eliminations [Member]
Revenue
Total Revenue	216		220		650		643
Adjusted PTC
External Adjusted Pre-tax Contribution	(127)	[1]	(148)	[1]	(408)	[1]	(465)	[1]
Assets
Total Assets	1,766				1,766				1,927
Corporate Other And Other Eliminations [Member] | Intersegment Eliminations [Member]
Revenue
Total Revenue	(1)		(2)		(5)		(3)
Adjusted PTC
External Adjusted Pre-tax Contribution	(1)	[1]	6	[1]	19	[1]	38	[1]
Corporate Other And Other Eliminations [Member] | Operating Segments [Member]
Revenue
Total Revenue	217		222		655		646
Adjusted PTC
External Adjusted Pre-tax Contribution	(126)	[1]	(154)	[1]	(427)	[1]	(503)	[1]
Discontinued Operations [Member]
Assets
Total Assets	$ 1,609				$ 1,609				$ 1,727

[1] Adjusted pre-tax 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.