Investment securities (Details Textual) (USD $)	3 Months Ended	6 Months Ended			3 Months Ended		6 Months Ended		3 Months Ended
	Jun. 30, 2011	Jun. 30, 2012 Investment	Jun. 30, 2011	Dec. 31, 2011	Jun. 30, 2012 Mortgage-backed securities [Member]	Jun. 30, 2011 Mortgage-backed securities [Member]	Jun. 30, 2012 Mortgage-backed securities [Member]	Jun. 30, 2011 Mortgage-backed securities [Member]	Jun. 30, 2011 Collateralized Debt Obligations [Member]	Jun. 30, 2011 Trust preferred securities [Member]	Mar. 31, 2011 Government issued or guaranteed [Member]
Investment Holdings [Line Items]
Pre-tax other-than temporary impairment losses					$ 16,000,000	$ 27,000,000	$ 28,000,000	$ 43,000,000
Aggregate amortized cost on mortgage-backed securities						1,000,000,000		1,000,000,000	100,000,000	136,000,000	484,000,000
Pre-tax gain on sale of mortgage-backed securities						66,000,000			20,000,000	25,000,000	39,000,000
Investment securities (Textual) [Abstract]
Gross realized gains on investment securities	111,000,000		150,000,000
Gross realized losses on investment securities	0		0
Number of investment securities with aggregate gross unrealized losses		290
Unrealized losses on individual investment securities		324,387,000		393,032,000
Unrealized losses on privately issued residential mortgage-backed securities		288,000,000
Privately issued mortgage backed securities at cost		1,400,000,000
Unrealized losses on trust preferred securities issued by financial institutions and securities backed by trust preferred securities		33,000,000
Other debt securities at cost		133,000,000
Other, fair value		$ 334,781,000		$ 366,886,000