Financial Instruments Owned and Pledged as Collateral at Fair Value, Securities Purchased Under Agreements to Resell and Securities Sold Under Agreements to Repurchase - Additional Information (Detail)	9 Months Ended
	Sep. 30, 2015
Banking and Thrift [Abstract]
Securities average estimated maturity period (in years)	8 months 16 days
Confidence Level Value At Risk	98.00%
Value At Risk Threshold	0.10%