Investments (Fixed Maturities Securities Excluding Investments Classified as Trading) (Details) - USD ($) $ in Thousands	Jun. 30, 2022	Dec. 31, 2021
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	$ 16,197,708	$ 12,737,749
Allowance for Credit Losses	4,810	4,149
Fair Value	14,438,956	13,278,166
Fixed maturities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	16,197,708	12,737,749
Gross Unrealized Gain	48,573	658,544
Gross Unrealized Losses	1,802,515	113,978
Allowance for Credit Losses	4,810	4,149
Fair Value	14,438,956	13,278,166
Fixed maturities \| US Treasury securities and obligations of U.S. government authorities and agencies
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	636,878	303,040
Gross Unrealized Gain	1,921	31,011
Gross Unrealized Losses	44,925	111
Allowance for Credit Losses	0	0
Fair Value	593,874	333,940
Fixed maturities \| Obligations of U.S. states and their political subdivisions
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	569,296	584,244
Gross Unrealized Gain	5,347	46,978
Gross Unrealized Losses	20,633	701
Allowance for Credit Losses	0	0
Fair Value	554,010	630,521
Fixed maturities \| Foreign government bonds
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	319,719	324,454
Gross Unrealized Gain	705	29,299
Gross Unrealized Losses	51,864	3,271
Allowance for Credit Losses	116	11
Fair Value	268,444	350,471
Fixed maturities \| U.S. public corporate securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	6,034,911	4,794,878
Gross Unrealized Gain	29,418	366,764
Gross Unrealized Losses	736,312	29,770
Allowance for Credit Losses	0	0
Fair Value	5,328,017	5,131,872
Fixed maturities \| U.S. private corporate securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	2,509,630	1,964,767
Gross Unrealized Gain	6,792	59,037
Gross Unrealized Losses	228,868	16,880
Allowance for Credit Losses	1,831	2,049
Fair Value	2,285,723	2,004,875
Fixed maturities \| Foreign public corporate securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	1,222,452	906,031
Gross Unrealized Gain	2,629	34,234
Gross Unrealized Losses	136,018	10,363
Allowance for Credit Losses	0	0
Fair Value	1,089,063	929,902
Fixed maturities \| Foreign private corporate securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	3,140,859	2,741,449
Gross Unrealized Gain	190	62,932
Gross Unrealized Losses	503,503	48,381
Allowance for Credit Losses	2,863	2,089
Fair Value	2,634,683	2,753,911
Fixed maturities \| Asset-backed securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	925,707	547,549
Gross Unrealized Gain	322	860
Gross Unrealized Losses	31,476	1,099
Allowance for Credit Losses	0	0
Fair Value	894,553	547,310
Fixed maturities \| Commercial mortgage-backed securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	740,060	552,653
Gross Unrealized Gain	723	25,928
Gross Unrealized Losses	46,095	3,397
Allowance for Credit Losses	0	0
Fair Value	694,688	575,184
Fixed maturities \| Residential mortgage-backed securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	98,196	18,684
Gross Unrealized Gain	526	1,501
Gross Unrealized Losses	2,821	5
Allowance for Credit Losses	0	0
Fair Value	$ 95,901	$ 20,180

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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