Schedule of Contractual Maturities of Debt Securities Available for Sale (Detail) - USD ($) $ in Millions	Dec. 31, 2015	Dec. 31, 2014
Investments, Debt and Equity Securities [Abstract]
Due within one year, Amortized Cost	$ 438
Due after one year through five years, Amortized Cost	1,829
Due after five years through ten years, Amortized Cost	1,244
Due after ten years, Amortized Cost	2,304
Mortgage and asset-backed securities, Amortized Cost	3,203
Amortized Cost	9,018	$ 9,072
Due within one year, Fair Value	439
Due after one year through five years, Fair Value	1,871
Due after five years through ten years, Fair Value	1,264
Due after ten years, Fair Value	2,384
Mortgage and asset-backed securities, Fair Value	3,152
Total debt securities, Fair Value	$ 9,110	$ 9,547