Regulatory Matters - Additional Information (Detail) - USD ($) $ in Billions	1 Months Ended	9 Months Ended
	Jan. 31, 2016	Sep. 30, 2015	Dec. 31, 2014
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Common equity tier one capital ratio		4.50%
Tier 1 risk based capital ratios		6.00%	4.00%
Total risk based capital ratio		8.00%
Tier 1 leverage ratio		4.00%
Capital conservation buffer ratio		2.50%
Total assets		$ 15.0
Common equity tier 1 capital assets		250.0
Bank [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Total assets		$ 10.0
Scenario, Forecast [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Tier 1 risk based capital ratios	8.50%
Total risk based capital ratio	10.50%
Common equity Tier 1 risk-based capital ratio	7.00%
Minimum capital conservation buffer	0.625%