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Investment Securities - Additional Information (Detail) - USD ($)
3 Months Ended
Mar. 31, 2019
Dec. 31, 2018
Debt Securities, Available-for-sale [Line Items]    
Credit-related impairment loss on investment securities held-to-maturity $ 0  
Investment securities pledged as collateral $ 1,530,000,000 $ 1,660,000,000
United States [Member]    
Debt Securities, Available-for-sale [Line Items]    
Securities issued by U.S. government percentage 89.00%