Other Material Contingencies - Total Guarantees (Detail) (USD $) In Millions, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012
Guarantor Obligations [Line Items]
Total guarantees, by type and term	$ 1,272	$ 859
Energy transactions [Member]
Guarantor Obligations [Line Items]
Total guarantees, by type and term	782
Solar energy projects [Member]
Guarantor Obligations [Line Items]
Total guarantees, by type and term	447
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	27
0 - 3 years [Member]
Guarantor Obligations [Line Items]
Total guarantees, by type and term	1,191
0 - 3 years [Member] | Energy transactions [Member]
Guarantor Obligations [Line Items]
Total guarantees, by type and term	705
0 - 3 years [Member] | Solar energy projects [Member]
Guarantor Obligations [Line Items]
Total guarantees, by type and term	443
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	27
4 - 10 years [Member]
Guarantor Obligations [Line Items]
Total guarantees, by type and term	52
4 - 10 years [Member] | Energy transactions [Member]
Guarantor Obligations [Line Items]
Total guarantees, by type and term	52
4 - 10 years [Member] | Solar energy projects [Member]
Guarantor Obligations [Line Items]
Total guarantees, by type and term
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	29
Greater than 10 years [Member] | Energy transactions [Member]
Guarantor Obligations [Line Items]
Total guarantees, by type and term	25
Greater than 10 years [Member] | Solar energy projects [Member]
Guarantor Obligations [Line Items]
Total guarantees, by type and term	4
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