Commitments and contingencies (Details) (USD $)			6 Months Ended
	Jun. 30, 2011	Dec. 31, 2010	Jun. 30, 2011 2011 - 2013 [Member]	Jun. 30, 2011 2014 - 2017 [Member]
Commitments to extend credit
Home equity lines of credit	$ 6,534,722,000	$ 6,281,366,000
Commercial real estate loans to be sold	181,180,000	72,930,000
Other commercial real estate and construction	2,746,493,000	1,672,006,000
Residential real estate loans to be sold	482,774,000	161,583,000
Other residential real estate	113,738,000	151,111,000
Commercial and other	10,787,826,000	8,332,199,000
Standby letters of credit	3,963,575,000	3,917,318,000
Commercial letters of credit	65,766,000	76,962,000
Financial guarantees and indemnification contracts	1,790,502,000	1,609,944,000
Commitments to sell real estate loans	903,582,000	734,696,000
Naming rights of football stadium per year			5,000,000	6,000,000
Commitments and contingencies (Textuals) [Abstract]
Maximum credit risk for recourse associated with loans sold under Federal National Mortgage Association Delegated Underwriting and Servicing program	1,700,000,000	1,600,000,000
Outstanding loan principal balances reinsured	78,000,000
Assets of subsidiaries providing reinsurance to satisfy claims	51,000,000
Range of reasonably possible losses, minimum	0
Range of reasonably possible losses, maximum	$ 40,000,000