Other Material Contingencies (Total Guarantees) (Details) (USD $) In Millions, unless otherwise specified	Mar. 31, 2012	Dec. 31, 2011
Guarantor Obligations [Line Items]
Total guarantees, by type and term	$ 760	$ 760
Energy Transactions [Member]
Guarantor Obligations [Line Items]
Total guarantees, by type and term	707
Intra-Company Guarantees [Member]
Guarantor Obligations [Line Items]
Total guarantees, by type and term	16
Other Guarantees [Member]
Guarantor Obligations [Line Items]
Total guarantees, by type and term	37
Guarantee Duration, 0 - 3 Years [Member]
Guarantor Obligations [Line Items]
Total guarantees, by type and term	685
Guarantee Duration, 0 - 3 Years [Member] | Energy Transactions [Member]
Guarantor Obligations [Line Items]
Total guarantees, by type and term	637
Guarantee Duration, 0 - 3 Years [Member] | Intra-Company Guarantees [Member]
Guarantor Obligations [Line Items]
Total guarantees, by type and term	15
Guarantee Duration, 0 - 3 Years [Member] | Other Guarantees [Member]
Guarantor Obligations [Line Items]
Total guarantees, by type and term	33
Guarantee Duration, 4 - 10 Years [Member]
Guarantor Obligations [Line Items]
Total guarantees, by type and term	8
Guarantee Duration, 4 - 10 Years [Member] | Energy Transactions [Member]
Guarantor Obligations [Line Items]
Total guarantees, by type and term	4
Guarantee Duration, 4 - 10 Years [Member] | Other Guarantees [Member]
Guarantor Obligations [Line Items]
Total guarantees, by type and term	4
Guarantee Duration, Greater Than 10 Years [Member]
Guarantor Obligations [Line Items]
Total guarantees, by type and term	67
Guarantee Duration, Greater Than 10 Years [Member] | Energy Transactions [Member]
Guarantor Obligations [Line Items]
Total guarantees, by type and term	66
Guarantee Duration, Greater Than 10 Years [Member] | Intra-Company Guarantees [Member]
Guarantor Obligations [Line Items]
Total guarantees, by type and term	$ 1