Comprehensive Income - Components of Other Comprehensive Income (Loss) and Amounts Reclassified from Accumulated Other Comprehensive Income (Loss) to Net Income (Detail) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance, before tax		$ (569,328)	$ (493,290)	$ (485,245)
Unrealized holding gains (losses), net, before tax		247,411	(121,589)	(15,005)
Foreign currency translation adjustment, before tax		1,381	(2,817)	4,447
Unrealized losses on cash flow hedges, before tax		160,373	(4,965)	(12,291)
Current year benefit plans gains, before tax		(126,618)	19,871	9,276
Total other comprehensive income (loss), before tax		282,547	(109,500)	(13,573)
Amortization of unrealized holding losses on held-to-maturity ("HTM") securities, before tax		3,394	4,252	3,387
Gains realized in net income, before tax		3	(18)	(21,279)
Accretion of net gain (losses) on terminated cash flow hedges, before tax		(136)	(111)	(137)
Net yield adjustment from cash flow hedges currently in effect, before tax		(13,011)	13,339	(3,916)
Amortization of prior service credit, before tax		(4,173)	(4,172)	(802)
Amortization of actuarial losses, before tax		20,745	(42,967)	28,275
Total other comprehensive income (loss), before tax		289,369	(53,243)	(8,045)
Reclassification of income tax effects to retained earnings				(64,029)
Ending balance, before tax		(279,959)	(569,328)	(493,290)
Cumulative effect of change in accounting principles — equity securities, before tax	[1]		(22,795)
Amortization of actuarial (loss) gain		(20,745)	42,967	(28,275)
Beginning balance, tax		149,247	129,476	190,609
Unrealized holding gains (losses), net, tax		(65,009)	31,946	7,269
Foreign currency translation adjustment, tax		(290)	592	(2,206)
Unrealized losses on cash flow hedges, tax		(42,163)	1,306	4,837
Current year benefit plans gains, tax		33,287	(5,224)	(3,650)
Total other comprehensive income (loss), tax		(74,175)	28,620	6,250
Amortization of unrealized holding losses on held-to-maturity ('HTM') securities, tax		(892)	(1,118)	(1,333)
Gains realized in net income, tax		(1)	4	7,195
Accretion of net gain on terminated cash flow hedges, tax		36	29	54
Net yield adjustment from cash flow hedges currently in effect, tax		3,421	(3,507)	1,541
Amortization of prior service credit, tax		1,097	1,097	315
Amortization of actuarial losses, tax		(5,454)	(11,296)	(11,126)
Total other comprehensive income (loss), tax		(75,968)	13,829	2,896
Reclassification of income tax effects to retained earnings, tax				(64,029)
Ending balance, tax		73,279	149,247	129,476
Cumulative effect of change in accounting principles — equity securities, tax	[1]		5,942
Beginning balance, net of tax		(420,081)	(363,814)	(294,636)
Unrealized holding gains (losses), net of tax		182,402	(89,643)	(7,736)
Foreign currency translation adjustments		1,091	(2,225)	2,241
Unrealized losses on cash flow hedges, net of tax		118,210	(3,659)	(7,454)
Current year benefit plans gains, net of tax		(93,331)	14,647	5,626
Total other comprehensive income (loss) before reclassifications, net of tax		208,372	(80,880)	(7,323)
Amortization of unrealized holding losses on held-to-maturity ('HTM') securities, net of tax		2,502	3,134	2,054
Gains realized in net income, net of tax		2	(14)	(14,084)
Accretion of net gain on terminated cash flow hedges, net of tax		(100)	(82)	(83)
Net yield adjustment from cash flow hedges currently in effect, net of tax		(9,590)	9,832	(2,375)
Amortization of prior service credit, net of tax		(3,076)	(3,075)	(487)
Amortization of actuarial losses, net of tax		15,291	31,671	17,149
Total other comprehensive income (loss)		213,401	(39,414)	(5,149)
Ending balance, net of tax		(206,680)	(420,081)	(363,814)
Cumulative effect of change inaccounting principle — equity securities	[1]		(16,853)
Reclassification of income tax effects to retained earnings, before tax				(64,029)
Gains realized in net income, net of tax		2	(14)	(14,084)
Investment Securities [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance, before tax		(200,107)	(59,957)
Unrealized holding gains (losses), net, before tax		247,411	(121,589)
Total other comprehensive income (loss), before tax		247,411	(121,589)
Amortization of unrealized holding losses on held-to-maturity ("HTM") securities, before tax		3,394	4,252
Gains realized in net income, before tax		3	(18)
Total other comprehensive income (loss), before tax		250,808	(117,355)
Reclassification of income tax effects to retained earnings				8,065
Ending balance, before tax		50,701	(200,107)	(59,957)
Cumulative effect of change in accounting principles — equity securities, before tax	[1]		(22,795)
Total other comprehensive income (loss)		184,906	(86,523)	(19,766)
Cumulative effect of change inaccounting principle — equity securities			(16,853)
Reclassification of income tax effects to retained earnings, before tax				8,065
Defined Benefit Plans [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance, before tax		(354,502)	(413,168)	(449,917)
Current year benefit plans gains, before tax		(126,618)	19,871	9,276
Total other comprehensive income (loss), before tax		(126,618)	19,871	9,276
Amortization of prior service credit, before tax		(4,173)	(4,172)	(802)
Amortization of actuarial losses, before tax		20,745	(42,967)	28,275
Total other comprehensive income (loss), before tax		(110,046)	58,666	36,749
Reclassification of income tax effects to retained earnings				53,960
Ending balance, before tax		(464,548)	(354,502)	(413,168)
Amortization of actuarial (loss) gain		(20,745)	42,967	(28,275)
Total other comprehensive income (loss)		(81,116)	43,243	22,288
Reclassification of income tax effects to retained earnings, before tax				53,960
Other [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance, before tax		(14,719)	(20,165)	(8,268)
Foreign currency translation adjustment, before tax		1,381	(2,817)	4,447
Unrealized losses on cash flow hedges, before tax		160,373	(4,965)	(12,291)
Total other comprehensive income (loss), before tax		161,754	(7,782)	(7,844)
Accretion of net gain (losses) on terminated cash flow hedges, before tax		(136)	(111)	(137)
Net yield adjustment from cash flow hedges currently in effect, before tax		(13,011)	13,339	(3,916)
Total other comprehensive income (loss), before tax		148,607	5,446	(11,897)
Ending balance, before tax		$ 133,888	(14,719)	(20,165)
Investment Securities With OTTI [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance, before tax			19,628	46,725
Unrealized holding gains (losses), net, before tax				(8,746)
Total other comprehensive income (loss), before tax				(8,746)
Gains realized in net income, before tax				(18,351)
Total other comprehensive income (loss), before tax				(27,097)
Ending balance, before tax				19,628
Investment Securities All Other [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance, before tax			$ (79,585)	(73,785)
Unrealized holding gains (losses), net, before tax				(6,259)
Total other comprehensive income (loss), before tax				(6,259)
Amortization of unrealized holding losses on held-to-maturity ("HTM") securities, before tax				3,387
Gains realized in net income, before tax				(2,928)
Total other comprehensive income (loss), before tax				(5,800)
Ending balance, before tax				$ (79,585)

[1] Beginning January 1, 2018, equity securities with readily determinable market values are required to be measured at fair value with changes in fair value recognized in the income statement. Prior to that date, such changes in fair value were reflected in other comprehensive income. Separate presentation of investment securities with an other-than-temporary impairment change is no longer required.