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Available-for-Sale and Held-to-Maturity Securities (Parenthetical) (Detail) - USD ($)
$ in Millions
Sep. 30, 2015
Dec. 31, 2014
Investment Holdings [Line Items]    
FHLB, restricted stock holdings $ 248 $ 248
Federal Reserve Bank, restricted stock holdings 354 352
Available-for-sale and other securities [1] 28,799 22,408
Interest-Only Mortgage-Backed Securities    
Investment Holdings [Line Items]    
Available-for-sale and other securities $ 53 $ 175
[1] Amortized cost of $27,986 and $21,677 at September 30, 2015 and December 31, 2014, respectively.