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, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance, before tax			$ (85,143)	$ (279,959)
Unrealized holding gains (losses), net, before tax			(57,388)	151,777
Foreign currency translation adjustment, before tax			(1,246)	(222)
Unrealized gains on cash flow hedges, before tax			821	508,226
Total other comprehensive income (loss) before reclassifications			(57,813)	659,781
Amortization of unrealized holding losses on held-to-maturity ("HTM") securities, before tax			3,333	2,678
Gains realized in net income			(8)	(3)
Accretion of net gain (losses) on terminated cash flow hedges, before tax			(90)	(94)
Net yield adjustment from cash flow hedges currently in effect, before tax			(206,713)	(183,598)
Amortization of prior service credit, before tax			(3,139)	(3,140)
Amortization of actuarial losses, before tax			65,792	42,080
Total other comprehensive income (loss), before tax			(198,638)	517,704
Ending balance, before tax	$ (283,781)	$ 237,745	(283,781)	237,745
Beginning balance, tax			22,111	73,279
Unrealized holding gains (losses), net, tax			15,124	(39,277)
Foreign currency translation adjustment, tax			360	(39)
Unrealized gains on cash flow hedges, tax			(214)	(131,504)
Total other comprehensive income (loss) before reclassifications			15,270	(170,820)
Amortization of unrealized holding losses on held-to-maturity ('HTM') securities, tax			(871)	(725)
Gains realized in net income, tax			2	1
Accretion of net gain on terminated cash flow hedges, tax			24	26
Net yield adjustment from cash flow hedges currently in effect, tax			53,997	47,506
Amortization of prior service credit, tax			860	927
Amortization of actuarial losses, tax			(18,031)	(12,436)
Total other comprehensive income (loss), tax			51,251	(135,521)
Ending balance, tax	73,362	(62,242)	73,362	(62,242)
Beginning balance, net of tax			(63,032)	(206,680)
Unrealized holding gains (losses), net of tax			(42,264)	112,500
Foreign currency translation adjustments	(1,579)	2,733	(886)	(261)
Unrealized gains on cash flow hedges, net of tax			607	376,722
Total other comprehensive income (loss) before reclassifications			(42,543)	488,961
Amortization of unrealized holding losses on held-to-maturity ('HTM') securities, net of tax			2,462	1,953
Gains realized in net income, net of tax			(6)	(2)
Accretion of net gain on terminated cash flow hedges, net of tax			(66)	(68)
Net yield adjustment from cash flow hedges currently in effect, net of tax			(152,716)	(136,092)
Amortization of prior service credit, net of tax			(2,279)	(2,213)
Amortization of actuarial losses, net of tax			47,761	29,644
Total other comprehensive income (loss)	(33,445)	(69,127)	(147,387)	382,183
Ending balance, net of tax	(210,419)	175,503	(210,419)	175,503
Investment Securities [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance, before tax			195,386	50,701
Unrealized holding gains (losses), net, before tax			(57,388)	151,777
Total other comprehensive income (loss) before reclassifications			(57,388)	151,777
Amortization of unrealized holding losses on held-to-maturity ("HTM") securities, before tax			3,333	2,678
Gains realized in net income			(8)	(3)
Total other comprehensive income (loss), before tax			(54,063)	154,452
Ending balance, before tax	141,323	205,153	141,323	205,153
Total other comprehensive income (loss)			(39,808)
Defined Benefit Plans [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance, before tax			(650,087)	(464,548)
Amortization of prior service credit, before tax			(3,139)	(3,140)
Amortization of actuarial losses, before tax			65,792	42,080
Total other comprehensive income (loss), before tax			62,653	38,940
Ending balance, before tax	(587,434)	(425,608)	(587,434)	(425,608)
Total other comprehensive income (loss)			45,482
Other [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance, before tax			369,558	133,888
Foreign currency translation adjustment, before tax			(1,246)	(222)
Unrealized gains on cash flow hedges, before tax			821	508,226
Total other comprehensive income (loss) before reclassifications			(425)	508,004
Accretion of net gain (losses) on terminated cash flow hedges, before tax			(90)	(94)
Net yield adjustment from cash flow hedges currently in effect, before tax			(206,713)	(183,598)
Total other comprehensive income (loss), before tax			(207,228)	324,312
Ending balance, before tax	$ 162,330	$ 458,200	$ 162,330	$ 458,200