Available-for-Sale and Held-to-Maturity Securities (Parenthetical) (Detail) (USD $) In Millions, unless otherwise specified	Sep. 30, 2014		Dec. 31, 2013
Investment Holdings [Line Items]
FHLB, restricted stock holdings	$ 249		$ 402
Federal Reserve Bank, restricted stock holdings	351		349
Available-for-sale and other securities	22,912	[1]	18,597	[1]
Interest-Only Mortgage-Backed Securities
Investment Holdings [Line Items]
Available-for-sale and other securities	$ 192		$ 262

[1] Amortized cost of $22,392 and $18,409 at September 30, 2014 and December 31, 2013, respectively.