Derivative financial instruments (Details 2) (USD $) In Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2011	Jun. 30, 2010	Jun. 30, 2011	Jun. 30, 2010
Information about fair values of derivative instruments in consolidated statement of income
Derivatives in fair value hedging relationships, derivatives	$ 21,945	$ 43,653	$ 9,540	$ 55,924
Derivatives in fair value hedging relationships, hedged item	(21,145)	(41,376)	(9,097)	(53,158)
Derivatives not designated as hedging instruments, derivatives	258	111	185	(161)
Derivatives not designated as hedging instruments, hedged item	0
Interest rate contracts [Member]
Information about fair values of derivative instruments in consolidated statement of income
Derivatives not designated as hedging instruments, derivatives	1,001	(504)	1,476	(1,118)
Derivatives not designated as hedging instruments, hedged item			0
Foreign exchange and other option and futures contracts [Member]
Information about fair values of derivative instruments in consolidated statement of income
Derivatives not designated as hedging instruments, derivatives	(743)	615	(1,291)	957
Derivatives not designated as hedging instruments, hedged item			0
Fixed rate time deposits [Member]
Information about fair values of derivative instruments in consolidated statement of income
Derivatives in fair value hedging relationships, derivatives		(304)		(503)
Derivatives in fair value hedging relationships, hedged item		304		503
Fixed rate long-term borrowings [Member]
Information about fair values of derivative instruments in consolidated statement of income
Derivatives in fair value hedging relationships, derivatives	21,945	43,957	9,540	56,427
Derivatives in fair value hedging relationships, hedged item	$ (21,145)	$ (41,680)	$ (9,097)	$ (53,661)