Commitments and Contingencies (Details) (USD $)	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011
Commitments and Contingencies
Total outstanding loan balances	$ 15,849,299,000	$ 13,791,239,000
Fair value of risk participation guaranteed obligations	400,000	300,000
Maximum liability under indemnity in connection with liquidation of an investment acquired	23,000,000
Settlement from arbitration on a legal claim	4,800,000
Net charges included in other operating expense in noninterest expense	4,500,000	300,000
Commitments and Contingencies
Commitments
Off-balance sheet loan commitments
Commitments and Contingencies
Commitments	6,480,000,000	5,670,000,000
Letters of Credit
Commitments and Contingencies
Commitments	765,000,000	723,500,000
Standby letters of credit, included within letters of credit
Commitments and Contingencies
Commitments	659,200,000	609,800,000
Commercial letters of credit, including within letters of credit
Commitments and Contingencies
Commitments	105,800,000	113,700,000
Private equity fund and alternative investment
Commitments and Contingencies
Commitments	68,900,000	68,900,000
Commitments, funded amount	61,300,000	57,900,000
Affordable housing fund
Commitments and Contingencies
Commitments	$ 58,600,000	$ 39,600,000