Supplemental Information about Changes to Accumulated Other Comprehensive Income - Schedule of Change in Balance by Component (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Increase (Decrease) in AOCI, Net of Tax
Beginning balance	$ 8,771,092	$ 7,294,307	$ 5,415,177
Other comprehensive income (loss) before reclassifications, net of tax	(343,041)	1,145,356	1,529,591
Reclassifications, net of tax	(8,620)	39,058	(4,236)
Other comprehensive income (loss)	(351,661)	1,184,414	1,525,355
Ending balance	8,642,806	8,771,092	7,294,307
Total
Increase (Decrease) in AOCI, Net of Tax
Beginning balance	3,029,244	1,844,830	319,475
Ending balance	2,677,583	3,029,244	1,844,830
Available for Sale Assets
Increase (Decrease) in AOCI, Net of Tax
Beginning balance	3,175,572	1,982,650	435,698
Other comprehensive income (loss) before reclassifications, net of tax	(385,231)	1,167,003	1,557,883
Reclassifications, net of tax	(25,051)	25,919	(10,931)
Other comprehensive income (loss)	(410,282)	1,192,922	1,546,952
Ending balance	2,765,290	3,175,572	1,982,650
Deferred Acquisition Costs
Increase (Decrease) in AOCI, Net of Tax
Beginning balance	(4,704)	(5,916)	(4,163)
Other comprehensive income (loss) before reclassifications, net of tax	1,286	1,212	(1,753)
Reclassifications, net of tax	0	0	0
Other comprehensive income (loss)	1,286	1,212	(1,753)
Ending balance	(3,418)	(4,704)	(5,916)
Foreign Exchange
Increase (Decrease) in AOCI, Net of Tax
Beginning balance	23,302	12,058	6,495
Other comprehensive income (loss) before reclassifications, net of tax	(3,915)	11,244	5,563
Reclassifications, net of tax	0	0	0
Other comprehensive income (loss)	(3,915)	11,244	5,563
Ending balance	19,387	23,302	12,058
Pension Adjustments
Increase (Decrease) in AOCI, Net of Tax
Beginning balance	(164,926)	(143,962)	(118,555)
Other comprehensive income (loss) before reclassifications, net of tax	44,819	(34,103)	(32,102)
Reclassifications, net of tax	16,431	13,139	6,695
Other comprehensive income (loss)	61,250	(20,964)	(25,407)
Ending balance	$ (103,676)	$ (164,926)	$ (143,962)