Comprehensive Income - Accumulated Other Comprehensive Income (Loss), Net (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2022	Mar. 31, 2021
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance	$ 17,903,405	$ 16,187,283
Net gain (loss) during period	(249,807)	(75,446)
Ending balance	17,876,020	16,446,508
Investment Securities [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance	77,625
Net gain (loss) during period	(136,367)
Ending balance	(58,742)
Defined Benefit Plans [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance	(267,145)
Net gain (loss) during period	2,269
Ending balance	(264,876)
Accumulated Other Adjustment [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance	61,942
Net gain (loss) during period	(115,709)
Ending balance	(53,767)
Accumulated Other Comprehensive Income (Loss), Net [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance	(127,578)	(63,032)
Net gain (loss) during period	(249,807)
Ending balance	$ (377,385)	$ (138,478)