Comprehensive Income - Components of Other Comprehensive Income (Loss) and Amounts Reclassified from Accumulated Other Comprehensive Income (Loss) to Net Income (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance, before tax			$ (414,545)	$ (297,843)
Unrealized holding gains (losses), before tax			236,378	(79,932)
Foreign currency translation adjustment, before tax			(2,489)	(779)
Gains on cash flow hedges, before tax				1,453
Total other comprehensive income(loss) before reclassifications, before tax			233,889	(79,258)
Accretion of unrealized holding losses on held-to-maturity ("HTM") securities, before tax			2,081	1,589
Gains realized in net income, before tax			(268)	108
Accretion of net gain on terminated cash flow hedges, before tax			(77)	(63)
Amortization of prior service credit, before tax			(2,294)	(3,682)
Amortization of actuarial losses, before tax			15,103	22,465
Total reclassifications, before tax			14,545	20,417
Total gain (loss) during the period, before tax			248,434	(58,841)
Ending balance, before tax	$ (166,111)	$ (356,684)	(166,111)	(356,684)
Beginning balance, tax			162,918	116,849
Unrealized holding gains (losses), tax			(93,010)	31,617
Foreign currency translation adjustment, tax			871	261
Gains on cash flow hedges, tax				(568)
Total other comprehensive income(loss) before reclassifications, tax			(92,139)	31,310
Accretion of unrealized holding losses on held-to-maturity ("HTM") securities, tax			(819)	(621)
Gains realized in net income, tax			102	(40)
Accretion of net gain on terminated cash flow hedges, tax			30	25
Amortization of prior service credit, tax			902	1,640
Amortization of actuarial losses, tax			(5,904)	(9,981)
Total reclassifications, tax			(5,689)	(8,977)
Total gain (loss) during the period, tax			(97,828)	22,333
Ending balance, tax	65,090	139,182	65,090	139,182
Beginning balance			(251,627)	(180,994)
Unrealized holding gains (losses), net of tax			143,368	(48,315)
Foreign currency translation adjustment, net of tax	(1,565)	1,866	(1,618)	(518)
Gains on cash flow hedges, net of tax				885
Total other comprehensive income(loss) before reclassifications, net of tax			141,750	(47,948)
Accretion of unrealized holding losses on held-to-maturity ("HTM") securities, net of tax			1,262	968
Gains realized in net income, net of tax			(166)	68
Accretion of net gain on terminated cash flow hedges, net of tax			(47)	(38)
Amortization of prior service credit, net of tax			(1,392)	(2,042)
Amortization of actuarial losses, net of tax			9,199	12,484
Total reclassifications, net of tax			8,856	11,440
Total other comprehensive income (loss)	49,168	(65,011)	150,606	(36,508)
Ending balance	(101,021)	(217,502)	(101,021)	(217,502)
Investment Securities With OTTI [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance, before tax			16,359	7,438
Unrealized holding gains (losses), before tax			9,260	5,670
Total other comprehensive income(loss) before reclassifications, before tax			9,260	5,670
Total gain (loss) during the period, before tax			9,260	5,670
Ending balance, before tax	25,619	13,108	25,619	13,108
Investment Securities All Other [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance, before tax			62,849	201,828
Unrealized holding gains (losses), before tax			227,118	(85,602)
Total other comprehensive income(loss) before reclassifications, before tax			227,118	(85,602)
Accretion of unrealized holding losses on held-to-maturity ("HTM") securities, before tax			2,081	1,589
Gains realized in net income, before tax			(268)	108
Total reclassifications, before tax			1,813	1,697
Total gain (loss) during the period, before tax			228,931	(83,905)
Ending balance, before tax	291,780	117,923	291,780	117,923
Defined Benefit Plans [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance, before tax			(489,660)	(503,027)
Amortization of prior service credit, before tax			(2,294)	(3,682)
Amortization of actuarial losses, before tax			15,103	22,465
Total reclassifications, before tax			12,809	18,783
Total gain (loss) during the period, before tax			12,809	18,783
Ending balance, before tax	(476,851)	(484,244)	(476,851)	(484,244)
Beginning balance			(296,979)
Total other comprehensive income (loss)			7,807
Ending balance	(289,172)		(289,172)
Other [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance, before tax			(4,093)	(4,082)
Foreign currency translation adjustment, before tax			(2,489)	(779)
Gains on cash flow hedges, before tax				1,453
Total other comprehensive income(loss) before reclassifications, before tax			(2,489)	674
Accretion of net gain on terminated cash flow hedges, before tax			(77)	(63)
Total reclassifications, before tax			(77)	(63)
Total gain (loss) during the period, before tax			(2,566)	611
Ending balance, before tax	$ (6,659)	$ (3,471)	$ (6,659)	$ (3,471)