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, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance			$ (297,843)	$ (105,797)
Unrealized holding gains (losses), net			(1,440)	121,301
Foreign currency translation adjustment			(735)	(2,314)
Unrealized Gains (losses) on cash flow hedges			1,453	(162)
Total other comprehensive income before reclassifications			(722)	118,825
Accretion of unrealized holding losses on held-to-maturity ("HTM") securities			2,417	2,540
Losses realized in net income			108
Accretion of net gain on terminated cash flow hedges			(102)
Amortization of prior service credit			(5,523)	(5,933)
Amortization of actuarial losses			33,698	10,871
Total reclassifications			30,598	7,478
Total gain (loss) during the period			29,876	126,303
Ending balance	$ (267,967)	$ 20,506	(267,967)	20,506
Beginning balance			116,849	41,638
Unrealized holding gains (losses), net			952	(47,615)
Foreign currency translation adjustment			214	810
Unrealized Gains (losses) on cash flow hedges			(568)	64
Total other comprehensive income before reclassifications			598	(46,741)
Accretion of unrealized holding losses on held-to-maturity ("HTM") securities			(944)	(997)
Losses realized in net income			(40)
Accretion of net gain on terminated cash flow hedges			40
Amortization of prior service credit			2,359	2,328
Amortization of actuarial losses			(14,368)	(4,267)
Total reclassifications			(12,953)	(2,936)
Total gain (loss) during the period			(12,355)	(49,677)
Ending balance	104,494	(8,039)	104,494	(8,039)
Beginning balance			(180,994)	(64,159)
Unrealized holding gains (losses), net			(488)	73,686
Foreign currency translation adjustment	(3)	(1,817)	(521)	(1,504)
Unrealized Gains (losses) on cash flow hedges			885	(98)
Total other comprehensive income before reclassifications			(124)	72,084
Accretion of unrealized holding losses on held-to-maturity ("HTM") securities			1,473	1,543
Losses realized in net income			68
Accretion of net gain on terminated cash flow hedges			(62)
Amortization of prior service credit			(3,164)	(3,605)
Amortization of actuarial losses			19,330	6,604
Total reclassifications			17,645	4,542
Total gain (loss) during the period			17,521	76,626
Ending balance	(163,473)	12,467	(163,473)	12,467
Investment Securities With OTTI [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance			7,438	37,255
Unrealized holding gains (losses), net			9,699	12,038
Total other comprehensive income before reclassifications			9,699	12,038
Accretion of unrealized holding losses on held-to-maturity ("HTM") securities				1
Total reclassifications				1
Total gain (loss) during the period			9,699	12,039
Ending balance	17,137	49,294	17,137	49,294
Investment Securities All Other [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance			201,828	18,450
Unrealized holding gains (losses), net			(11,139)	109,263
Total other comprehensive income before reclassifications			(11,139)	109,263
Accretion of unrealized holding losses on held-to-maturity ("HTM") securities			2,417	2,539
Losses realized in net income			108
Total reclassifications			2,525	2,539
Total gain (loss) during the period			(8,614)	111,802
Ending balance	193,214	130,252	193,214	130,252
Defined Benefit Plans [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance			(503,027)	(161,617)
Amortization of prior service credit			(5,523)	(5,933)
Amortization of actuarial losses			33,698	10,871
Total reclassifications			28,175	4,938
Total gain (loss) during the period			28,175	4,938
Ending balance	(474,852)	(156,679)	(474,852)	(156,679)
Beginning balance			(305,589)
Total gain (loss) during the period			16,166
Ending balance	(289,423)		(289,423)
Other [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance			(4,082)	115
Foreign currency translation adjustment			(735)	(2,314)
Unrealized Gains (losses) on cash flow hedges			1,453	(162)
Total other comprehensive income before reclassifications			718	(2,476)
Accretion of net gain on terminated cash flow hedges			(102)
Total reclassifications			(102)
Total gain (loss) during the period			616	(2,476)
Ending balance	$ (3,466)	$ (2,361)	$ (3,466)	$ (2,361)