Comprehensive Income - Accumulated Other Comprehensive Income (Loss), Net (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance	$ 16,187,283	$ 15,716,649	$ 15,460,191
Net gain (loss) during period	(64,546)	143,648	213,401
Ending balance	17,903,405	16,187,283	15,716,649
Investment Securities [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance	144,602	37,380	(147,526)
Net gain (loss) during period	(66,977)	107,222	184,906
Ending balance	77,625	144,602	37,380
Defined Benefit Plans [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance	(481,064)	(342,419)	(261,303)
Net gain (loss) during period	213,919	(138,645)	(81,116)
Ending balance	(267,145)	(481,064)	(342,419)
Accumulated Other Adjustment [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance	273,430	98,359	(11,252)
Net gain (loss) during period	(211,488)	175,071	109,611
Ending balance	61,942	273,430	98,359
Accumulated Other Comprehensive Income (Loss), Net [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance	(63,032)	(206,680)	(420,081)
Net gain (loss) during period	(64,546)	143,648	213,401
Ending balance	$ (127,578)	$ (63,032)	$ (206,680)