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Securities (Investment Securities) (Parenthetical) (Detail) - USD ($)
$ in Millions
Mar. 31, 2018
Dec. 31, 2017
Investment Holdings    
FHLB, restricted stock holdings $ 248 $ 248
FRB, restricted stock holdings 362 362
Available-for-sale debt and other securities [1] 31,819 31,751
DTCC, restricted stock holdings $ 2 2
Interest-Only Mortgage-Backed Securities    
Investment Holdings    
Available-for-sale debt and other securities   $ 34
[1]

Amortized cost of $ 32,230 and $ 31,577 at March 31, 2018 and December 31, 2017 , respectively.