Schedule of Contractual Maturities of Debt Securities Available for Sale (Detail) (USD $) In Millions, unless otherwise specified	Sep. 30, 2014	Dec. 31, 2013
Available-for-sale Securities, Debt Maturities [Abstract]
Due within one year, Amortized Cost	$ 1,030
Due after one year through five years, Amortized Cost	2,119
Due after five years through ten years, Amortized Cost	2,184
Due after ten years, Amortized Cost	1,950
Mortgage and asset-backed securities, Amortized Cost	2,300
Amortized Cost	9,583	9,550
Due within one year, Fair Value	1,036
Due after one year through five years, Fair Value	2,234
Due after five years through ten years, Fair Value	2,307
Due after ten years, Fair Value	2,134
Mortgage and asset-backed securities, Fair Value	2,324
Total debt securities, Fair Value	$ 10,035	$ 9,800