Fair value measurements (Details 2) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009	Dec. 31, 2008
Financial assets:
Cash and cash equivalents	$ 1,452,397	$ 933,755	$ 1,246,342	$ 1,568,151
Interest-bearing deposits at banks	154,960	101,222
Trading account assets	561,834	523,834
Investment securities	7,673,154	7,150,540
Loans and leases:
Residential real estate loans	7,889,569	5,876,413
Consumer loans	12,020,229	11,483,564
Allowance for credit losses	(908,290)	(902,941)	(878,022)	(787,904)
Loans and leases, net	59,187,715	51,087,441
Financial liabilities:
Noninterest-bearing deposits	(20,017,883)	(14,557,568)
Time deposits	(6,107,530)	(5,817,170)
Deposits at Cayman Islands office	(355,927)	(1,605,916)
Short term borrowings	(782,082)	(947,432)	(2,442,582)
Long-term borrowings	(6,686,226)	(7,840,151)
Carrying Amount [Member]
Financial assets:
Cash and cash equivalents	1,452,397	933,755
Interest-bearing deposits at banks	154,960	101,222
Trading account assets	561,834	523,834
Investment securities	7,673,154	7,150,540
Loans and leases:
Commercial loans and leases	15,734,436	13,390,610
Commercial real estate loans	24,411,114	21,183,161
Residential real estate loans	7,923,165	5,928,056
Consumer loans	12,027,290	11,488,555
Allowance for credit losses	(908,290)	(902,941)
Loans and leases, net	59,187,715	51,087,441
Accrued interest receivable	222,618	202,182
Financial liabilities:
Noninterest-bearing deposits	(20,017,883)	(14,557,568)
Savings Deposits And NOW Accounts	(32,913,309)	(27,824,630)
Time deposits	(6,107,530)	(5,817,170)
Deposits at Cayman Islands office	(355,927)	(1,605,916)
Short term borrowings	(782,082)	(947,432)
Long-term borrowings	(6,686,226)	(7,840,151)
Accrued interest payable	(67,900)	(71,954)
Trading account liabilities	(434,559)	(333,222)
Other financial instruments:
Commitments to originate real estate loans for sale	6,923	2,244
Commitments to sell real estate loans	(3,498)	12,178
Other credit-related commitments	(109,828)	(74,426)
Interest rate swap agreements used for interest rate risk management	147,302	96,637
Calculated Estimate [Member]
Financial assets:
Cash and cash equivalents	1,452,397	933,755
Interest-bearing deposits at banks	154,960	101,222
Trading account assets	561,834	523,834
Investment securities	7,608,008	7,051,454
Loans and leases:
Commercial loans and leases	15,507,342	13,135,569
Commercial real estate loans	24,024,585	20,840,346
Residential real estate loans	7,782,935	5,699,028
Consumer loans	11,869,813	11,178,583
Allowance for credit losses	0	0
Loans and leases, net	59,184,675	50,853,526
Accrued interest receivable	222,618	202,182
Financial liabilities:
Noninterest-bearing deposits	(20,017,883)	(14,557,568)
Savings Deposits And NOW Accounts	(32,913,309)	(27,824,630)
Time deposits	(6,133,806)	(5,865,779)
Deposits at Cayman Islands office	(355,927)	(1,605,916)
Short term borrowings	(782,082)	(947,432)
Long-term borrowings	(6,720,174)	(7,937,397)
Accrued interest payable	(67,900)	(71,954)
Trading account liabilities	(434,559)	(333,222)
Other financial instruments:
Commitments to originate real estate loans for sale	6,923	2,244
Commitments to sell real estate loans	(3,498)	12,178
Other credit-related commitments	(109,828)	(74,426)
Interest rate swap agreements used for interest rate risk management	$ 147,302	$ 96,637