Schedule of Contractual Maturities of Debt Securities Available for Sale (Detail) (USD $) In Millions, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012
Investments Classified by Contractual Maturity Date [Line Items]
Due within one year, Amortized Cost	$ 460
Due after one year through five years, Amortized Cost	2,041
Due after five years through ten years, Amortized Cost	2,778
Due after ten years, Amortized Cost	1,816
Mortgage and asset-backed securities, Amortized Cost	2,595
Total debt securities, Amortized Cost	9,690	9,119
Due within one year, Fair Value	464
Due after one year through five years, Fair Value	2,123
Due after five years through ten years, Fair Value	2,902
Due after ten years, Fair Value	1,884
Mortgage and asset-backed securities, Fair Value	2,626
Total debt securities, Fair Value	$ 9,999	$ 9,847