Other Material Contingencies - Total Guarantees (Detail) (USD $) In Millions, unless otherwise specified	Jun. 30, 2013	Dec. 31, 2012
Guarantor Obligations [Line Items]
Total guarantees, by type and term	$ 883	$ 859
Energy transactions [Member]
Guarantor Obligations [Line Items]
Total guarantees, by type and term	836
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	31
0 - 3 years [Member]
Guarantor Obligations [Line Items]
Total guarantees, by type and term	824
0 - 3 years [Member] | Energy transactions [Member]
Guarantor Obligations [Line Items]
Total guarantees, by type and term	777
0 - 3 years [Member] | Intra-company guarantees [Member]
Guarantor Obligations [Line Items]
Total guarantees, by type and term	16
0 - 3 years [Member] | Other guarantees [Member]
Guarantor Obligations [Line Items]
Total guarantees, by type and term	31
4 - 10 years [Member]
Guarantor Obligations [Line Items]
Total guarantees, by type and term	31
4 - 10 years [Member] | Energy transactions [Member]
Guarantor Obligations [Line Items]
Total guarantees, by type and term	31
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
Greater than 10 years [Member]
Guarantor Obligations [Line Items]
Total guarantees, by type and term	28
Greater than 10 years [Member] | Energy transactions [Member]
Guarantor Obligations [Line Items]
Total guarantees, by type and term	28
Greater than 10 years [Member] | Intra-company guarantees [Member]
Guarantor Obligations [Line Items]
Total guarantees, by type and term
Greater than 10 years [Member] | Other guarantees [Member]
Guarantor Obligations [Line Items]
Total guarantees, by type and term