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 (Details)	12 Months Ended
	Dec. 31, 2017
Banking and Thrift [Abstract]
Securities Average Estimated Maturity Period (in years)	1 year 6 months
Confidence Level Value at Risk (as a percent)	98.00%
Value at Risk Threshold (as a percent)	0.10%