Other Material Contingencies - Total Guarantees (Detail) (USD $) In Millions, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Guarantor Obligations [Line Items]
Total guarantees, by type and term	$ 859	$ 760
Energy transactions [Member]
Guarantor Obligations [Line Items]
Total guarantees, by type and term	803
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	40
0 - 3 years [Member]
Guarantor Obligations [Line Items]
Total guarantees, by type and term	766
0 - 3 years [Member] | Energy transactions [Member]
Guarantor Obligations [Line Items]
Total guarantees, by type and term	716
0 - 3 years [Member] | Intra-company guarantees [Member]
Guarantor Obligations [Line Items]
Total guarantees, by type and term	15
0 - 3 years [Member] | Other guarantees [Member]
Guarantor Obligations [Line Items]
Total guarantees, by type and term	35
4 - 10 years [Member]
Guarantor Obligations [Line Items]
Total guarantees, by type and term	30
4 - 10 years [Member] | Energy transactions [Member]
Guarantor Obligations [Line Items]
Total guarantees, by type and term	25
4 - 10 years [Member] | Intra-company guarantees [Member]
Guarantor Obligations [Line Items]
Total guarantees, by type and term
4 - 10 years [Member] | Other guarantees [Member]
Guarantor Obligations [Line Items]
Total guarantees, by type and term	5
Greater than 10 years [Member]
Guarantor Obligations [Line Items]
Total guarantees, by type and term	63
Greater than 10 years [Member] | Energy transactions [Member]
Guarantor Obligations [Line Items]
Total guarantees, by type and term	62
Greater than 10 years [Member] | Intra-company guarantees [Member]
Guarantor Obligations [Line Items]
Total guarantees, by type and term	1
Greater than 10 years [Member] | Other guarantees [Member]
Guarantor Obligations [Line Items]
Total guarantees, by type and term