Commitments and contingencies (Details) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2012	Dec. 31, 2011
Commitments to extend credit
Home equity lines of credit	$ 6,369,114	$ 6,393,332
Commercial real estate loans to be sold	134,471	177,982
Other commercial real estate and construction	3,138,855	2,818,071
Residential real estate loans to be sold	771,278	182,474
Other residential real estate	438,197	129,466
Commercial and other	10,004,023	10,442,754
Standby letters of credit	3,811,819	3,930,271
Commercial letters of credit	56,725	44,981
Financial guarantees and indemnification contracts	1,895,755	1,903,254
Commitments to sell real estate loans	$ 1,068,940	$ 635,899