Off-Balance Sheet Arrangements, Guarantees and Other Commitments - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Commitments and Contingencies Disclosure [Line Items]
Rent expense for premises and equipment leased under operating leases	$ 14.5	$ 11.9	$ 11.5
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
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	5.5	6.1
Collateral in the form of cash	309
Collateral in the form of investment securities	$ 8.0