Derivative financial instruments (Details 1) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2012	Dec. 31, 2011
Information about fair values of derivative instruments in consolidated balance sheet
Asset derivatives, fair value	$ 644,741	$ 619,001
Liability derivatives, fair value	444,456	440,685
Designated as Hedging Instrument [Member]
Information about fair values of derivative instruments in consolidated balance sheet
Asset derivatives, fair value	150,393	147,534
Liability derivatives, fair value	5,274	2,287
Not Designated as Hedging Instrument [Member]
Information about fair values of derivative instruments in consolidated balance sheet
Asset derivatives, fair value	494,348	471,467
Liability derivatives, fair value	439,182	438,398
Interest rate swap agreements [Member] | Designated as Hedging Instrument [Member]
Information about fair values of derivative instruments in consolidated balance sheet
Asset derivatives, fair value	149,947	147,302
Liability derivatives, fair value	0
Commitments to sell real estate loans [Member] | Designated as Hedging Instrument [Member]
Information about fair values of derivative instruments in consolidated balance sheet
Asset derivatives, fair value	446	232
Liability derivatives, fair value	5,274	2,287
Commitments to sell real estate loans [Member] | Not Designated as Hedging Instrument [Member]
Information about fair values of derivative instruments in consolidated balance sheet
Asset derivatives, fair value	992	1,328
Liability derivatives, fair value	9,021	2,771
Mortgage-related commitments to originate real estate loans for sale [Member] | Not Designated as Hedging Instrument [Member]
Information about fair values of derivative instruments in consolidated balance sheet
Asset derivatives, fair value	34,111	7,991
Liability derivatives, fair value	60	1,068
Interest rate contracts [Member] | Not Designated as Hedging Instrument [Member]
Information about fair values of derivative instruments in consolidated balance sheet
Asset derivatives, fair value	439,617	443,033
Liability derivatives, fair value	409,653	415,836
Foreign exchange and other option and futures contracts [Member] | Not Designated as Hedging Instrument [Member]
Information about fair values of derivative instruments in consolidated balance sheet
Asset derivatives, fair value	19,628	19,115
Liability derivatives, fair value	$ 20,448	$ 18,723