Off-Balance Sheet Arrangements, Guarantees and Other Commitments - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2015
Venture capital and private equity fund investments
Commitments and Contingencies Disclosure [Line Items]
Commitments to invest, period from the inception of the fund	10 years
Call unrestricted, percentage of committed capital	100.00%
Venture capital and private equity fund investments | Lower Limit
Commitments and Contingencies Disclosure [Line Items]
Expected commitment period to invest in venture capital and private equity funds (in years)	5 years
Venture capital and private equity fund investments | Upper Limit
Commitments and Contingencies Disclosure [Line Items]
Expected commitment period to invest in venture capital and private equity funds (in years)	7 years
Standby Letter of Credit
Commitments and Contingencies Disclosure [Line Items]
Deferred fees	8.2
Collateral in the form of cash	509
Collateral in the form of investment securities	1.5