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Minimum Regulatory Capital Requirements - Additional Information (Detail)
Jan. 01, 2019
Dec. 31, 2015
Dec. 31, 2014
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]      
Minimum ratio of capital to risk-weighted assets   8.00% 8.00%
Minimum leverage ratio calculated as ratio of Tier 1 capital to average quarterly assets   11.91% 11.70%
Scenario, Forecast [Member]      
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]      
Capital conservation buffer 2.50%    
CapitalRequiredForCapitalAdequacyToRiskWeightedAssets 10.50%    
Minimum ratio of capital to risk-weighted assets 8.00%    
Minimum leverage ratio calculated as ratio of Tier 1 capital to average quarterly assets 4.00%    
Capital conservation buffer at base level 0.625%    
Regulatory capital requirements phase period 4 years    
Scenario, Forecast [Member] | Common Equity Tier 1 Capital [Member]      
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]      
Minimum ratio of capital to risk-weighted assets 4.50%    
Capital conservation buffer 2.50%    
CapitalRequiredForCapitalAdequacyToRiskWeightedAssets 7.00%    
Scenario, Forecast [Member] | Tier 1 Capital [Member]      
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]      
Minimum ratio of capital to risk-weighted assets 6.00%    
CapitalRequiredForCapitalAdequacyToRiskWeightedAssets 8.50%