Other Material Contingencies (Total Guarantees) (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2011	Dec. 31, 2010
Guarantor Obligations [Line Items]
Total guarantees, by type and term	$ 760	$ 859
Financial And Performance Guarantee For Energy Transactions [Member]
Guarantor Obligations [Line Items]
Total guarantees, by type and term	706
Financial And Performance Guarantee For Intra-Company [Member]
Guarantor Obligations [Line Items]
Total guarantees, by type and term	16
Financial And Performance Guarantee Other [Member]
Guarantor Obligations [Line Items]
Total guarantees, by type and term	38
Guarantee Duration, 0-3 Years [Member]
Guarantor Obligations [Line Items]
Total guarantees, by type and term	680
Guarantee Duration, 0-3 Years [Member] | Financial And Performance Guarantee For Energy Transactions [Member]
Guarantor Obligations [Line Items]
Total guarantees, by type and term	640
Guarantee Duration, 0-3 Years [Member] | Financial And Performance Guarantee For Intra-Company [Member]
Guarantor Obligations [Line Items]
Total guarantees, by type and term	15
Guarantee Duration, 0-3 Years [Member] | Financial And Performance Guarantee Other [Member]
Guarantor Obligations [Line Items]
Total guarantees, by type and term	25
Guarantee Duration, 4-10 Years [Member]
Guarantor Obligations [Line Items]
Total guarantees, by type and term	16
Guarantee Duration, 4-10 Years [Member] | Financial And Performance Guarantee For Energy Transactions [Member]
Guarantor Obligations [Line Items]
Total guarantees, by type and term	3
Guarantee Duration, 4-10 Years [Member] | Financial And Performance Guarantee Other [Member]
Guarantor Obligations [Line Items]
Total guarantees, by type and term	13
Guarantee Duration, Greater Than 10 Years [Member]
Guarantor Obligations [Line Items]
Total guarantees, by type and term	64
Guarantee Duration, Greater Than 10 Years [Member] | Financial And Performance Guarantee For Energy Transactions [Member]
Guarantor Obligations [Line Items]
Total guarantees, by type and term	63
Guarantee Duration, Greater Than 10 Years [Member] | Financial And Performance Guarantee For Intra-Company [Member]
Guarantor Obligations [Line Items]
Total guarantees, by type and term	$ 1