Comprehensive income (Details) (USD $) In Thousands	9 Months Ended
	Sep. 30, 2011	Sep. 30, 2010
Available for sale ("AFS") investment securities with other-than-temporary impairment ("OTTI"):
Unrealized holding losses, net, net, before-tax amount	$ (35,305)	$ (67,052)
Unrealized holding losses, net, income taxes	13,952	26,074
Unrealized holding losses, net, net of tax amount	(21,353)	(40,978)
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	(41,713)	(58,714)
Less: OTTI charges recognized in net income, income taxes	16,372	22,758
Less: OTTI charges recognized in net income, net	(25,341)	(35,956)
Net change for AFS investment securities with OTTI, before tax	2,594	(8,338)
Net change for AFS investment securities with OTTI, income taxes	(923)	3,316
Net change for AFS investment securities with OTTI, after tax	1,671	(5,022)
AFS investment securities - all other:
Unrealized holding gains during period, net, before-tax amount	147,338	233,174
Unrealized holding gains during period, net, income taxes	(57,629)	(91,018)
Unrealized holding gains during period, net, net of tax amount	89,709	142,156
Less: reclassification adjustment for gains realized in net income, before-tax amount	146,115	1,023
Less: Reclassification adjustment for gains realized in net income, income taxes	(57,257)	(392)
Less: Reclassification adjustment for gains realized in net income, net	88,858	631
Net change for AFS investment securities - all other, before tax	1,223	232,151
Net change for AFS investment securities - all other, tax	(372)	(90,626)
Net change for AFS investment securities - all other, after tax	851	141,525
Held-to-maturity ("HTM") investment securities with OTTI:
Unrealized holding gains on HTM securities, net, before-tax amount	(8,500)
Unrealized holding gains on HTM securities, net, income taxes	3,336
Unrealized holding gains on HTM securities, net, net of tax amount	(5,164)
Less: reclassification to income of unrealized holding losses, before tax	(213)
Less: reclassification to income of unrealized holding losses, tax	83
Less: reclassification to income of unrealized holding losses, net of tax	(130)
Less: OTTI charges recognized in net income, before tax	(10,500)
Less: OTTI charges recognized in net income, tax	4,121
Less: OTTI charges recognized in net income, net of tax	(6,379)
Net change for HTM investment securities with OTTI, before tax	2,213
Net change for HTM investment securities with OTTI, tax	(868)
Net change for HTM investment securities with OTTI, net of tax	1,345
Reclassification to income of unrealized holding losses on investment securities previously transferred from AFS to HTM, before tax	5,108	6,400
Reclassification to income of unrealized holding losses on investment securities previously transferred from AFS to HTM, Tax	(2,005)	(2,511)
Reclassification to income of unrealized holding losses on investment securities previously transferred from AFS to HTM, net of tax	3,103	3,889
Net unrealized gains (losses) on investment securities, before tax	11,138	230,213
Net unrealized gains (losses) on investment securities, income taxes	(4,168)	(89,821)
Net unrealized gains (losses) on investment securities, net of tax	6,970	140,392
Reclassification to income for amortization of gains on terminated cash flow hedges , before tax	(336)	(336)
Reclassification to income for amortization of gains on terminated cash flow hedges, income taxes	125	125
Reclassification to income for amortization of gains on terminated cash flow hedges , net of tax	(211)	(211)
Foreign currency translation adjustment, before tax	(779)
Foreign currency translation adjustment, tax	276
Foreign currency translation adjustment, net of tax	(503)
Defined benefit plans liability adjustment, before-tax amount	10,586	5,370
Defined benefit plans liability adjustment, income taxes	(4,155)	(2,108)
Defined benefit plans liability adjustment, net	6,431	3,262
Total Comprehensive Income, before-tax amount	20,609	235,247
Total Comprehensive Income, income taxes	(7,922)	(91,804)
Total Comprehensive Income, net	$ 12,687	$ 143,443