Pension Plans and Other Postretirement Benefits - Data Relating to Funding Position of Defined Benefit Plans (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Change in plan assets:
Fair value of plan assets at beginning of year	$ 2,418,702
Employer contributions		$ 300,000
Fair value of plan assets at end of year	2,593,533	2,418,702
Pension Benefits [Member]
Change in benefit obligation:
Benefit obligation at beginning of year	2,521,292	2,247,329
Service cost	20,513	19,944	$ 17,294
Interest cost	61,873	71,421	81,579
Actuarial (gain) loss	(69,230)	288,944
Benefits paid	(114,235)	(106,346)
Benefit obligation at end of year	2,420,213	2,521,292	2,247,329
Change in plan assets:
Fair value of plan assets at beginning of year	2,420,582	2,037,940
Actual return on plan assets	278,260	178,610
Employer contributions	11,231	310,378
Benefits paid	(114,235)	(106,346)
Fair value of plan assets at end of year	2,595,838	2,420,582	2,037,940
Funded status	175,625	(100,710)
Prepaid asset recognized in the consolidated balance sheet	332,197	64,670
Accrued liability recognized in the consolidated balance sheet	(156,572)	(165,380)
Net accrued asset (liability) recognized in the consolidated balance sheet	175,625	(100,710)
Net loss (gain)	391,721	684,780
Net prior service cost (credit)	724	1,277
Pre-tax adjustment to AOCI	392,445	686,057
Taxes	(101,447)	(178,375)
Net adjustment to AOCI	290,998	507,682
Other Postretirement Benefits [Member]
Change in benefit obligation:
Benefit obligation at beginning of year	55,281	56,492
Service cost	1,014	970	859
Interest cost	1,311	1,741	2,344
Plan participants’ contributions	2,553	2,386
Actuarial (gain) loss	(2,232)	2,371
Medicare Part D reimbursement	540	574
Benefits paid	(6,621)	(9,253)
Benefit obligation at end of year	51,846	55,281	$ 56,492
Change in plan assets:
Employer contributions	3,528	6,293
Plan participants’ contributions	2,553	2,386
Medicare Part D reimbursement	540	574
Benefits paid	(6,621)	(9,253)
Funded status	(51,846)	(55,281)
Accrued liability recognized in the consolidated balance sheet	(51,846)	(55,281)
Net accrued asset (liability) recognized in the consolidated balance sheet	(51,846)	(55,281)
Net loss (gain)	(14,638)	(13,701)
Net prior service cost (credit)	(17,531)	(22,269)
Pre-tax adjustment to AOCI	(32,169)	(35,970)
Taxes	8,316	9,352
Net adjustment to AOCI	$ (23,853)	$ (26,618)