Schedule of Contractual Maturities of Debt Securities Available for Sale (Detail) (USD $) In Millions, unless otherwise specified	Mar. 31, 2014	Dec. 31, 2013
Available-for-sale Securities, Debt Maturities [Abstract]
Due within one year, Amortized Cost	$ 477
Due after one year through five years, Amortized Cost	2,114
Due after five years through ten years, Amortized Cost	2,533
Due after ten years, Amortized Cost	1,953
Mortgage and asset-backed securities, Amortized Cost	2,596
Total debt securities, Amortized Cost	9,673	9,550
Due within one year, Fair Value	483
Due after one year through five years, Fair Value	2,214
Due after five years through ten years, Fair Value	2,663
Due after ten years, Fair Value	2,081
Mortgage and asset-backed securities, Fair Value	2,607
Total debt securities, Fair Value	$ 10,048	$ 9,800