Other Material Contingencies - Total Guarantees (Detail) (USD $)	Sep. 30, 2014	Dec. 31, 2013
Guarantor Obligations [Line Items]
Total guarantees, by type and term	$ 1,418,000,000	$ 1,331,000,000
Energy Transactions [Member]
Guarantor Obligations [Line Items]
Total guarantees, by type and term	881,000,000
Solar Energy Projects [Member]
Guarantor Obligations [Line Items]
Total guarantees, by type and term	507,000,000
Other [Member]
Guarantor Obligations [Line Items]
Total guarantees, by type and term	30,000,000
0 - 3 years [Member]
Guarantor Obligations [Line Items]
Total guarantees, by type and term	1,297,000,000
0 - 3 years [Member] | Energy Transactions [Member]
Guarantor Obligations [Line Items]
Total guarantees, by type and term	760,000,000
0 - 3 years [Member] | Solar Energy Projects [Member]
Guarantor Obligations [Line Items]
Total guarantees, by type and term	507,000,000
0 - 3 years [Member] | Other [Member]
Guarantor Obligations [Line Items]
Total guarantees, by type and term	30,000,000
4 - 10 years [Member]
Guarantor Obligations [Line Items]
Total guarantees, by type and term	25,000,000
4 - 10 years [Member] | Energy Transactions [Member]
Guarantor Obligations [Line Items]
Total guarantees, by type and term	25,000,000
Greater than 10 years [Member]
Guarantor Obligations [Line Items]
Total guarantees, by type and term	96,000,000
Greater than 10 years [Member] | Energy Transactions [Member]
Guarantor Obligations [Line Items]
Total guarantees, by type and term	$ 96,000,000