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Investment Securities - Amount of Gross Gains and Losses Realized through Sales of Available-for-sale Investment Securities (Detail) - USD ($)
$ in Millions
3 Months Ended 6 Months Ended
Jun. 30, 2016
Jun. 30, 2016
Jun. 30, 2015
Available-for-sale Securities, Gross Realized Gain (Loss), Excluding Other than Temporary Impairments [Abstract]      
Realized gains $ 16 $ 19 $ 1
Realized losses (12) (12) $ (1)
Net realized gains (losses) 4 7  
Income tax (benefit) on net realized gains (losses) $ 2 $ 3