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, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance, before tax			$ (569,328)	$ (493,290)
Cumulative effect of change in accounting principle — equity securities, before tax				(22,795)
Unrealized holding gains (losses), net, before tax			237,615	(230,135)
Foreign currency translation adjustment, before tax			(2,663)	(1,783)
Unrealized gains (losses) on cash flow hedges, before tax			204,587	(26,522)
Total other comprehensive income (loss) before reclassifications, before tax			439,539	(258,440)
Amortization of unrealized holding losses on held-to-maturity ("HTM") securities, before tax			2,524	2,519
(Gains) losses realized in net income, before tax			7	(18)
Accretion of net gain on terminated cash flow hedges, before tax			(93)	(83)
Net yield adjustment from cash flow hedges currently in effect, before tax			6,693	7,650
Amortization of prior service credit, before tax			(3,129)	(3,129)
Amortization of actuarial losses, before tax			15,559	32,225
Total other comprehensive income (loss), before tax			461,100	(219,276)
Ending balance, before tax	$ (108,228)	$ (735,361)	(108,228)	(735,361)
Beginning balance, tax			149,247	129,476
Cumulative effect of change in accounting principle — equity securities, tax				5,942
Unrealized holding gains (losses), net, tax			(62,432)	60,494
Foreign currency translation adjustment, tax			559	374
Unrealized gains (losses) on cash flow hedges, tax			(53,786)	6,972
Total other comprehensive income (loss) before reclassifications, tax			(115,659)	67,840
Amortization of unrealized holding losses on held-to-maturity ('HTM') securities, tax			(663)	(662)
(Gains) losses realized in net income, tax			(2)	4
Accretion of net gain on terminated cash flow hedges, tax			25	22
Net yield adjustment from cash flow hedges currently in effect, tax			(1,760)	(2,011)
Amortization of prior service credit, tax			823	823
Amortization of actuarial losses, tax			(4,091)	(8,472)
Total other comprehensive income (loss), tax			(121,327)	57,544
Ending balance, tax	27,920	192,962	27,920	192,962
Beginning balance, net of tax			(420,081)	(363,814)
Cumulative effect of change in accounting principle — equity securities				(16,853)
Unrealized holding gains (losses), net of tax			175,183	(169,641)
Foreign currency translation adjustment	(1,704)	(265)	(2,104)	(1,409)
Unrealized gains (losses) on cash flow hedges, net of tax			150,801	(19,550)
Total other comprehensive income (loss) before reclassifications, net of tax			323,880	(190,600)
Amortization of unrealized holding losses on held-to-maturity ('HTM') securities, net of tax			1,861	1,857
(Gains) losses realized in net income, net of tax			5	(14)
Accretion of net gain on terminated cash flow hedges, net of tax			(68)	(61)
Net yield adjustment from cash flow hedges currently in effect, net of tax			4,933	5,639
Amortization of prior service credit, net of tax			(2,306)	(2,306)
Amortization of actuarial losses, net of tax			11,468	23,753
Total other comprehensive income (loss)	32,650	(24,458)	339,773	(161,732)
Ending balance, net of tax	(80,308)	(542,399)	(80,308)	(542,399)
Investment Securities [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance, before tax			(200,107)	(59,957)
Cumulative effect of change in accounting principle — equity securities, before tax				(22,795)
Unrealized holding gains (losses), net, before tax			237,615	(230,135)
Total other comprehensive income (loss) before reclassifications, before tax			237,615	(230,135)
Amortization of unrealized holding losses on held-to-maturity ("HTM") securities, before tax			2,524	2,519
(Gains) losses realized in net income, before tax			7	(18)
Total other comprehensive income (loss), before tax			240,146	(227,634)
Ending balance, before tax	40,039	(310,386)	40,039	(310,386)
Total other comprehensive income (loss)			177,049
Defined Benefit Plans [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance, before tax			(354,502)	(413,168)
Amortization of prior service credit, before tax			(3,129)	(3,129)
Amortization of actuarial losses, before tax			15,559	32,225
Total other comprehensive income (loss), before tax			12,430	29,096
Ending balance, before tax	(342,072)	(384,072)	(342,072)	(384,072)
Total other comprehensive income (loss)			9,162
Other [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance, before tax			(14,719)	(20,165)
Foreign currency translation adjustment, before tax			(2,663)	(1,783)
Unrealized gains (losses) on cash flow hedges, before tax			204,587	(26,522)
Total other comprehensive income (loss) before reclassifications, before tax			201,924	(28,305)
Accretion of net gain on terminated cash flow hedges, before tax			(93)	(83)
Net yield adjustment from cash flow hedges currently in effect, before tax			6,693	7,650
Total other comprehensive income (loss), before tax			208,524	(20,738)
Ending balance, before tax	$ 193,805	$ (40,903)	$ 193,805	$ (40,903)