Comprehensive income (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012	Jun. 30, 2011
Available-for-sale ("AFS") investment securities with other-than-temporary impairment ("OTTI"):
Unrealized holding losses, net, before-tax amount			$ (8,024)	$ (11,227)
Unrealized holding losses, net, income taxes			3,149	4,501
Unrealized holding losses, net, net of tax amount			(4,875)	(6,726)
Less: reclassification adjustment for gains realized in net income, before tax amount				3,814
Less: reclassification adjustment for gains realized in net income, income taxes				(1,497)
Less: reclassification adjustment for gains realized in net income, net				2,317
Less: OTTI charges recognized in net income, before tax amount			(22,304)	(32,071)
Less: OTTI charges recognized in net income, income taxes			8,754	12,587
Less: OTTI charges recognized in net income, net			(13,550)	(19,484)
Net change for AFS investment securities with OTTI, before tax			14,280	17,030
Net change for AFS investment securities with OTTI, income taxes			(5,605)	(6,589)
Net change for AFS investment securities with OTTI, after tax			8,675	10,441
AFS investment securities - all other:
Unrealized holding gains during period, net, before-tax amount			93,177	77,869
Unrealized holding gains during period, net, income taxes			(36,535)	(30,368)
Unrealized holding gains during period, net, net of tax amount			56,642	47,501
Less: reclassification adjustment for gains realized in net income, before-tax amount			(363)	146,115
Less: reclassification adjustment for gains realized in net income, income taxes			145	(57,257)
Less: reclassification adjustment for gains realized in net income, net			(218)	88,858
Net change for AFS investment securities - all other, before tax			93,540	(68,246)
Net change for AFS investment securities - all other, tax			(36,680)	26,889
Net change for AFS investment securities - all other, net of tax			56,860	(41,357)
Held-to-maturity ("HTM") investment securities with OTTI:
Unrealized holding gains on HTM securities, net, before-tax amount			(2,848)	(8,500)
Unrealized holding gains on HTM securities, net, income taxes			1,118	3,336
Unrealized holding gains on HTM securities, net, net of tax amount			(1,730)	(5,164)
Less: reclassification to income of unrealized holding losses, before tax			(1,497)	(12)
Less: reclassification to income of unrealized holding losses, tax			587	5
Less: reclassification to income of unrealized holding losses, net of tax			(910)	(7)
Less: OTTI charges recognized in net income, before tax			(5,355)	(10,500)
Less: OTTI charges recognized in net income, tax			2,102	4,121
Less: OTTI charges recognized in net income, net of tax			(3,253)	(6,379)
Net change for HTM investment securities with OTTI, before tax			4,004	2,012
Net change for HTM investment securities with OTTI, tax			(1,571)	(790)
Net change for HTM investment securities with OTTI, net of tax			2,433	1,222
Unrealized holding losses on investment securities previously transferred from AFS to HTM
Reclassification to income of unrealized holding losses on investment securities previously transferred from AFS to HTM, before tax			2,310	2,967
Reclassification to income of unrealized holding losses on investment securities previously transferred from AFS to HTM, Tax			(907)	(1,165)
Reclassification to income of unrealized holding losses on investment securities previously transferred from AFS to HTM, net of tax			1,403	1,802
Net unrealized gains (losses) on investment securities, before tax			114,134	(46,237)
Net unrealized gains (losses) on investment securities, income taxes			(44,763)	18,345
Net unrealized gains (losses) on investment securities, net of tax	49,289	(33,550)	69,371	(27,892)
Reclassification to income for amortization of gains on terminated cash flow hedges , before tax			(178)	(224)
Reclassification to income for amortization of gains on terminated cash flow hedges, income taxes			66	83
Reclassification to income for amortization of gains on terminated cash flow hedges	(42)	(71)	(112)	(141)
Foreign currency translation adjustment, before tax			(208)	313
Foreign currency translation adjustment, tax			77	(117)
Foreign currency translation adjustment, net of tax	(533)	196	(131)	196
Defined benefit plans liability adjustment, before tax amount			15,579	7,058
Defined benefit plans liability adjustment, income taxes			(6,115)	(2,770)
Defined benefit plans liability adjustment	4,695	2,177	9,464	4,288
Total Comprehensive Income, before-tax amount			129,327	(39,090)
Total Comprehensive Income, income taxes			(50,735)	15,541
Total other comprehensive income	$ 53,409	$ (31,248)	$ 78,592	$ (23,549)