Commitments (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Leases, Operating [Abstract]
Rental Expense Under Operating Lease Commitments	$ 58	$ 63	$ 56
OperatingLeasesFutureMinimumPaymentsDueAbstract
Future Minimum Lease Payments Under Operating Lease 2013	53
Future Minimum Lease Payments Under Operating Lease 2014	51
Future Minimum Lease Payments Under Operating Lease 2015	48
Future Minimum Lease Payments Under Operating Lease 2016	47
Future Minimum Lease Payments Under Operating Lease 2017	47
Future Minimum Lease Payments Under Operating Lease Thereafter	517
Future Minimum Lease Payments Under Operating Lease Total	763
Leases Capital [Abstract]
Gross Value Of Leased Assets	94	95
Capital Leases Future Minimum Payments Due [Abstract]
Future Minimum Lease Payments Under Capital Leases 2013	12
Future Minimum Lease Payments Under Capital Leases 2014	12
Future Minimum Lease Payments Under Capital Leases 2015	11
Future Minimum Lease Payments Under Capital Leases 2016	11
Future Minimum Lease Payments Under Capital Leases 2017	11
Future Minimum Lease Payments Under Capital Leases Thereafter	160
Future Minimum Lease Payments Under Capital Leases Total	217
Future Minimum Lease Payments Under Capital Leases Less Imputed	138
Present Value Of Total Minimum Lease Payments	79
Electricity Purchase Contracts [Member]
LongTermPurchaseCommitmentLineItems
Purchases Under Long Term Contracts	2,819	2,463	2,422
Future Commitments 2013	2,599
Future Commitments 2014	3,008
Future Commitments 2015	2,952
Future Commitments 2016	2,971
Future Commitments 2017	2,351
Future Commitments Thereafter	25,001
Future Commitments Total	38,882
Brazil Electricity Purchase Contracts Term Range	Electricity purchase contracts primarily include energy auction agreements at our Brazil subsidiaries with extended terms from 2013 through 2028
Fuel Purchase Contracts [Member]
LongTermPurchaseCommitmentLineItems
Purchases Under Long Term Contracts	1,860	1,577	1,686
Future Commitments 2013	1,555
Future Commitments 2014	998
Future Commitments 2015	555
Future Commitments 2016	428
Future Commitments 2017	416
Future Commitments Thereafter	4,618
Future Commitments Total	8,570
Other Purchase Contracts [Member]
LongTermPurchaseCommitmentLineItems
Purchases Under Long Term Contracts	1,701	1,767	1,652
Future Commitments 2013	1,976
Future Commitments 2014	1,743
Future Commitments 2015	1,629
Future Commitments 2016	1,202
Future Commitments 2017	1,093
Future Commitments Thereafter	11,153
Future Commitments Total	$ 18,796