Regulatory and Capital Requirements - Additional Information (Detail)	12 Months Ended
	Dec. 31, 2015		Jan. 01, 2019	Dec. 31, 2014
Schedule of Capitalization, Equity [Line Items]
Common equity Tier 1 capital to risk-weighted assets ratio	4.50%
Ratio of Tier 1 capital to risk-weighted assets	9.70%	[1]		9.70%
Risk-based Capital Minimum Capital Requirements, Ratio	8.00%	[1]		8.00%
Tier 1 Leverage Capital Minimum Capital Requirements, Ratio	4.00%	[1]		4.00%
Common equity Tier 1 capital conservation buffer, ratio	0.625%
Annual increase in Common equity Tier 1 capital conservation buffer, ratio	0.625%
Forecast [Member]
Schedule of Capitalization, Equity [Line Items]
Common equity Tier 1 capital conservation buffer, ratio			2.50%
Minimum [Member]
Schedule of Capitalization, Equity [Line Items]
Ratio of Tier 1 capital to risk-weighted assets	4.00%
Maximum [Member]
Schedule of Capitalization, Equity [Line Items]
Ratio of Tier 1 capital to risk-weighted assets	6.00%

[1] December 31, 2015 capital positions and ratios were calculated under Basel III rules which became effective January 1, 2015.