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		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance, before tax			$ (414,545)	$ (297,843)
Unrealized holding gains (losses), before tax			235,666	(1,440)
Foreign currency translation adjustment, before tax			(2,836)	(735)
Gains on cash flow hedges, before tax				1,453
Total other comprehensive income (loss) before reclassifications, before tax			232,830	(722)
Accretion of unrealized holding losses on held-to-maturity (“HTM”) securities, before tax			2,998	2,417
Gains (losses) realized in net income, before tax			(28,748)	108
Accretion of net gain on terminated cash flow hedges, before tax			(116)	(102)
Amortization of prior service credit, before tax			(3,440)	(5,523)
Amortization of actuarial losses, before tax			22,654	33,698
Total reclassifications, before tax			(6,652)	30,598
Total gain (loss) during the period, before tax			226,178	29,876
Ending balance, before tax	$ (188,367)	$ (267,967)	(188,367)	(267,967)
Beginning balance, tax			162,918	116,849
Unrealized holding gains (losses), tax			(92,714)	952
Foreign currency translation adjustment, tax			989	214
Gains on cash flow hedges, tax				(568)
Total other comprehensive income (loss) before reclassifications, tax			(91,725)	598
Accretion of unrealized holding losses on held-to-maturity (“HTM”) securities, tax			(1,180)	(944)
Gains (losses) realized in net income, tax			11,309	(40)
Accretion of net gain on terminated cash flow hedges, tax			46	40
Amortization of prior service credit, tax			1,354	2,359
Amortization of actuarial losses, tax			(8,914)	(14,368)
Total reclassifications, tax			2,615	(12,953)
Total gain (loss) during the period, tax			(89,110)	(12,355)
Ending balance, tax	73,808	104,494	73,808	104,494
Beginning balance			(251,627)	(180,994)
Unrealized holding gains (losses), net of tax			142,952	(488)
Foreign currency translation adjustment, net of tax	(229)	(3)	(1,847)	(521)
Gains on cash flow hedges, net of tax				885
Total other comprehensive income (loss) before reclassifications, net of tax			141,105	(124)
Accretion of unrealized holding losses on held-to-maturity ("HTM") securities, net of tax			1,818	1,473
Gains (losses) realized in net income, net of tax			(17,439)	68
Accretion of net gain on terminated cash flow hedges, net of tax			(70)	(62)
Amortization of prior service credit, net of tax			(2,086)	(3,164)
Amortization of actuarial losses, net of tax			13,740	19,330
Total reclassifications, net of tax			(4,037)	17,645
Total other comprehensive income (loss)	(13,538)	54,029	137,068	17,521
Ending balance	(114,559)	(163,473)	(114,559)	(163,473)
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			1,228	9,699
Total other comprehensive income (loss) before reclassifications, before tax			1,228	9,699
Total gain (loss) during the period, before tax			1,228	9,699
Ending balance, before tax	17,587	17,137	17,587	17,137
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			234,438	(11,139)
Total other comprehensive income (loss) before reclassifications, before tax			234,438	(11,139)
Accretion of unrealized holding losses on held-to-maturity (“HTM”) securities, before tax			2,998	2,417
Gains (losses) realized in net income, before tax			(28,748)	108
Total reclassifications, before tax			(25,750)	2,525
Total gain (loss) during the period, before tax			208,688	(8,614)
Ending balance, before tax	271,537	193,214	271,537	193,214
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			(3,440)	(5,523)
Amortization of actuarial losses, before tax			22,654	33,698
Total reclassifications, before tax			19,214	28,175
Total gain (loss) during the period, before tax			19,214	28,175
Ending balance, before tax	(470,446)	(474,852)	(470,446)	(474,852)
Total other comprehensive income (loss)			11,654
Other [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance, before tax			(4,093)	(4,082)
Foreign currency translation adjustment, before tax			(2,836)	(735)
Gains on cash flow hedges, before tax				1,453
Total other comprehensive income (loss) before reclassifications, before tax			(2,836)	718
Accretion of net gain on terminated cash flow hedges, before tax			(116)	(102)
Total reclassifications, before tax			(116)	(102)
Total gain (loss) during the period, before tax			(2,952)	616
Ending balance, before tax	$ (7,045)	$ (3,466)	$ (7,045)	$ (3,466)