Segments (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended				6 Months Ended				12 Months Ended
	Jun. 30, 2013		Jun. 30, 2012		Jun. 30, 2013 segment		Jun. 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	$ 4,340		$ 4,355		$ 8,895		$ 9,243
Intersegment	(272)		(266)		(562)		(568)
External Revenue	4,068		4,089		8,333		8,675
Adjusted PTC
Total Adjusted Pre-tax Contribution	271	[1]	206	[1]	536	[1]	619	[1]
Intersegment	0	[1]	0	[1]	0	[1]	0	[1]
External Adjusted Pre-tax Contribution	271	[1]	206	[1]	536	[1]	619	[1]
Reconciliation To Income From Continuing Operations Before Taxes
Unrealized derivative gains (losses)	65		(42)		52		(72)
Unrealized foreign currency gains (losses)	(15)		(41)		(42)		(12)
Disposition/acquisition gains	23		4		26		182
Impairment losses	0		(17)		(48)		(75)
Loss on extinguishment of debt	(164)		0		(207)		0
Pre-tax contribution	180		110		317		642
Add: income from continuing operations before taxes, attributable to noncontrolling interests	231		102		397		352
Less: Net equity in earnings of affiliates	2		11		6		24
INCOME FROM CONTINUING OPERATIONS BEFORE TAXES AND EQUITY IN EARNINGS OF AFFILIATES	409		201		708		970
Assets
Total Assets	40,836				40,836				41,830
US - Generation [Member]
Revenue
Total Revenue	190		216		360		414
Intersegment	0		0		0		0
External Revenue	190		216		360		414
Adjusted PTC
Total Adjusted Pre-tax Contribution	41	[1]	42	[1]	106	[1]	78	[1]
Intersegment	2	[1]	9	[1]	4	[1]	20	[1]
External Adjusted Pre-tax Contribution	43	[1]	51	[1]	110	[1]	98	[1]
Assets
Total Assets	3,157				3,157				3,259
US - Utilities [Member]
Revenue
Total Revenue	674		678		1,396		1,410
Intersegment	0		0		0		0
External Revenue	674		678		1,396		1,410
Adjusted PTC
Total Adjusted Pre-tax Contribution	24	[1]	32	[1]	94	[1]	89	[1]
Intersegment	1	[1]	1	[1]	1	[1]	1	[1]
External Adjusted Pre-tax Contribution	25	[1]	33	[1]	95	[1]	90	[1]
Assets
Total Assets	7,427				7,427				7,534
Andes - Generation [Member]
Assets
Total Assets	5,871				5,871				5,820
Andes - Gener - Generation [Member]
Revenue
Total Revenue	612		547		1,198		1,143
Intersegment	0		(9)		0		(18)
External Revenue	612		538		1,198		1,125
Adjusted PTC
Total Adjusted Pre-tax Contribution	57	[1]	24	[1]	131	[1]	119	[1]
Intersegment	3	[1]	(4)	[1]	5	[1]	(10)	[1]
External Adjusted Pre-tax Contribution	60	[1]	20	[1]	136	[1]	109	[1]
Andes - Other - Generation [Member]
Revenue
Total Revenue	112		223		217		361
Intersegment	(1)		0		(1)		0
External Revenue	111		223		216		361
Adjusted PTC
Total Adjusted Pre-tax Contribution	28	[1]	25	[1]	34	[1]	41	[1]
Intersegment	1	[1]	0	[1]	2	[1]	1	[1]
External Adjusted Pre-tax Contribution	29	[1]	25	[1]	36	[1]	42	[1]
Assets
Total Assets	754				754				799
Brazil - Generation [Member]
Revenue
Total Revenue	279		274		665		579
Intersegment	(250)		(248)		(530)		(530)
External Revenue	29		26		135		49
Adjusted PTC
Total Adjusted Pre-tax Contribution	66	[1]	45	[1]	106	[1]	97	[1]
Intersegment	(61)	[1]	(59)	[1]	(128)	[1]	(127)	[1]
External Adjusted Pre-tax Contribution	5	[1]	(14)	[1]	(22)	[1]	(30)	[1]
Assets
Total Assets	1,446				1,446				1,590
Brazil - Utilities [Member]
Revenue
Total Revenue	1,202		1,230		2,525		2,761
Intersegment	0		0		0		0
External Revenue	1,202		1,230		2,525		2,761
Adjusted PTC
Total Adjusted Pre-tax Contribution	11	[1]	9	[1]	13	[1]	65	[1]
Intersegment	41	[1]	40	[1]	86	[1]	86	[1]
External Adjusted Pre-tax Contribution	52	[1]	49	[1]	99	[1]	151	[1]
Assets
Total Assets	7,566				7,566				8,120
MCAC - Generation [Member]
Revenue
Total Revenue	471		426		929		819
Intersegment	0		0		(1)		(1)
External Revenue	471		426		928		818
Adjusted PTC
Total Adjusted Pre-tax Contribution	89	[1]	88	[1]	137	[1]	159	[1]
Intersegment	3	[1]	2	[1]	6	[1]	4	[1]
External Adjusted Pre-tax Contribution	92	[1]	90	[1]	143	[1]	163	[1]
Assets
Total Assets	4,434				4,434				4,293
EMEA - Generation [Member]
Revenue
Total Revenue	314		269		665		746
Intersegment	(20)		(8)		(28)		(17)
External Revenue	294		261		637		729
Adjusted PTC
Total Adjusted Pre-tax Contribution	64	[1]	55	[1]	158	[1]	242	[1]
Intersegment	(9)	[1]	(2)	[1]	(11)	[1]	(16)	[1]
External Adjusted Pre-tax Contribution	55	[1]	53	[1]	147	[1]	226	[1]
Assets
Total Assets	4,634				4,634				4,578
Asia - Generation [Member]
Revenue
Total Revenue	143		182		277		364
Intersegment	0		0		0		0
External Revenue	143		182		277		364
Adjusted PTC
Total Adjusted Pre-tax Contribution	40	[1]	55	[1]	71	[1]	87	[1]
Intersegment	0	[1]	1	[1]	1	[1]	1	[1]
External Adjusted Pre-tax Contribution	40	[1]	56	[1]	72	[1]	88	[1]
Assets
Total Assets	2,708				2,708				2,625
Corporate Other And Other Eliminations [Member]
Revenue
Total Revenue	343		310		663		646
Intersegment	(1)		(1)		(2)		(2)
External Revenue	342		309		661		644
Adjusted PTC
Total Adjusted Pre-tax Contribution	(149)	[1]	(169)	[1]	(314)	[1]	(358)	[1]
Intersegment	19	[1]	12	[1]	34	[1]	40	[1]
External Adjusted Pre-tax Contribution	(130)	[1]	(157)	[1]	(280)	[1]	(318)	[1]
Assets
Total Assets	2,839				2,839				3,010
Segment Discontinued Operations [Member]
Assets
Total Assets	$ 0				$ 0				$ 202

[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.