Investments - Summary of Fixed Maturities Available for Sale by Component (Detail) - USD ($) $ in Thousands	Sep. 30, 2022	Dec. 31, 2021
Debt Securities, Available-for-sale [Line Items]
Fair Value	$ 16,005,140	$ 21,305,287
Fixed maturities available for sale
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	18,173,471	17,805,309
Allowance for Credit Losses	0	(387)
Gross Unrealized Gains	182,301	3,534,404
Gross Unrealized Losses	(2,350,632)	(34,039)
Fair Value	$ 16,005,140	$ 21,305,287
Percentage of Fixed Maturities at Fair Value	100.00%	100.00%
U.S. Government direct, guaranteed, and government-sponsored enterprises \| Fixed maturities available for sale
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	$ 389,357	$ 383,083
Allowance for Credit Losses	0	0
Gross Unrealized Gains	2	64,513
Gross Unrealized Losses	(36,510)	(164)
Fair Value	$ 352,849	$ 447,432
Percentage of Fixed Maturities at Fair Value	2.00%	2.00%
States, municipalities, and political subdivisions \| Fixed maturities available for sale
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	$ 2,739,017	$ 2,252,997
Allowance for Credit Losses	0	0
Gross Unrealized Gains	24,724	239,135
Gross Unrealized Losses	(598,476)	(2,907)
Fair Value	$ 2,165,265	$ 2,489,225
Percentage of Fixed Maturities at Fair Value	14.00%	12.00%
Foreign governments \| Fixed maturities available for sale
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	$ 50,144	$ 59,861
Allowance for Credit Losses	0	0
Gross Unrealized Gains	42	900
Gross Unrealized Losses	(10,277)	(5,132)
Fair Value	$ 39,909	$ 55,629
Percentage of Fixed Maturities at Fair Value	0.00%	0.00%
Corporates \| Fixed maturities available for sale
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	$ 14,869,318	$ 14,967,902
Allowance for Credit Losses	0	(387)
Gross Unrealized Gains	143,654	3,199,104
Gross Unrealized Losses	(1,699,857)	(25,406)
Fair Value	$ 13,313,115	$ 18,141,213
Percentage of Fixed Maturities at Fair Value	83.00%	85.00%
Corporates \| Financial \| Fixed maturities available for sale
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	$ 4,818,454	$ 4,569,160
Allowance for Credit Losses	0	(387)
Gross Unrealized Gains	49,913	907,741
Gross Unrealized Losses	(552,378)	(9,349)
Fair Value	$ 4,315,989	$ 5,467,165
Percentage of Fixed Maturities at Fair Value	27.00%	26.00%
Corporates \| Utilities \| Fixed maturities available for sale
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	$ 1,906,747	$ 1,931,391
Allowance for Credit Losses	0	0
Gross Unrealized Gains	30,252	490,119
Gross Unrealized Losses	(144,762)	(1,012)
Fair Value	$ 1,792,237	$ 2,420,498
Percentage of Fixed Maturities at Fair Value	11.00%	11.00%
Corporates \| Energy \| Fixed maturities available for sale
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	$ 1,466,551	$ 1,587,892
Allowance for Credit Losses	0	0
Gross Unrealized Gains	14,281	346,780
Gross Unrealized Losses	(135,922)	(1,683)
Fair Value	$ 1,344,910	$ 1,932,989
Percentage of Fixed Maturities at Fair Value	8.00%	9.00%
Corporates \| Other corporate sectors \| Fixed maturities available for sale
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	$ 6,677,566	$ 6,879,459
Allowance for Credit Losses	0	0
Gross Unrealized Gains	49,208	1,454,464
Gross Unrealized Losses	(866,795)	(13,362)
Fair Value	$ 5,859,979	$ 8,320,561
Percentage of Fixed Maturities at Fair Value	37.00%	39.00%
Collateralized debt obligations \| Fixed maturities available for sale
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	$ 36,721	$ 36,468
Allowance for Credit Losses	0	0
Gross Unrealized Gains	13,874	27,037
Gross Unrealized Losses	0	0
Fair Value	$ 50,595	$ 63,505
Percentage of Fixed Maturities at Fair Value	0.00%	0.00%
Other asset-backed securities \| Fixed maturities available for sale
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	$ 88,914	$ 104,998
Allowance for Credit Losses	0	0
Gross Unrealized Gains	5	3,715
Gross Unrealized Losses	(5,512)	(430)
Fair Value	$ 83,407	$ 108,283
Percentage of Fixed Maturities at Fair Value	1.00%	1.00%

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Amount, before tax, of unrealized gain in accumulated other comprehensive income (AOCI) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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Amount, before tax, of unrealized loss in accumulated other comprehensive income (AOCI) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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Amount excluding accrued interest, of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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