Commitments and contingencies (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2011	Dec. 31, 2010
Commitments to extend credit
Home equity lines of credit	$ 6,393,332	$ 6,281,366
Commercial real estate loans to be sold	177,982	72,930
Other commercial real estate and construction	2,818,071	1,672,006
Residential real estate loans to be sold	182,474	161,583
Other residential real estate	129,466	151,111
Commercial and other	10,442,754	8,332,199
Standby letters of credit	3,930,271	3,917,318
Commercial letters of credit	44,981	76,962
Financial guarantees and indemnification contracts	1,903,254	1,609,944
Commitments to sell real estate loans	$ 635,899	$ 734,696