Available-for-Sale and Held-to-Maturity Securities (Parenthetical) (Detail) (USD $) In Millions, unless otherwise specified	Sep. 30, 2013		Dec. 31, 2012
Investment Holdings
FHLB, restricted stock holdings	$ 497		$ 497
Federal Reserve Bank, restricted stock holdings	349		347
Available-for-sale and other securities	18,080	[1]	15,207	[1]
Interest-Only-Strip [Member]
Investment Holdings
Available-for-sale and other securities	$ 279		$ 408

[1] Amortized cost of $17,665 and $14,571 at September 30, 2013 and December 31, 2012, respectively.