Investments (Fixed Maturities Securities Excluding Investments Classified as Trading) (Details) - USD ($) $ in Thousands	Dec. 31, 2022	Dec. 31, 2021
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	$ 21,311,087	$ 12,737,749
Allowance for Credit Losses	4,769	4,149
Fair Value	19,025,401	13,278,166
Fixed maturities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	21,311,087	12,737,749
Gross Unrealized Gains	72,582	658,544
Gross Unrealized Losses	2,353,499	113,978
Allowance for Credit Losses	4,769	4,149
Fair Value	19,025,401	13,278,166
Fixed maturities \| U.S. Treasury securities and obligations of U.S. government authorities and agencies
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	354,348	303,040
Gross Unrealized Gains	300	31,011
Gross Unrealized Losses	72,856	111
Allowance for Credit Losses	0	0
Fair Value	281,792	333,940
Fixed maturities \| Obligations of U.S. states and their political subdivisions
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	654,884	584,244
Gross Unrealized Gains	4,275	46,978
Gross Unrealized Losses	30,959	701
Allowance for Credit Losses	0	0
Fair Value	628,200	630,521
Fixed maturities \| Foreign government bonds
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	330,967	324,454
Gross Unrealized Gains	1,140	29,299
Gross Unrealized Losses	58,640	3,271
Allowance for Credit Losses	5	11
Fair Value	273,462	350,471
Fixed maturities \| U.S. public corporate securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	7,414,790	4,794,878
Gross Unrealized Gains	21,299	366,764
Gross Unrealized Losses	992,145	29,770
Allowance for Credit Losses	0	0
Fair Value	6,443,944	5,131,872
Fixed maturities \| U.S. private corporate securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	4,140,734	1,964,767
Gross Unrealized Gains	13,071	59,037
Gross Unrealized Losses	335,205	16,880
Allowance for Credit Losses	1,871	2,049
Fair Value	3,816,729	2,004,875
Fixed maturities \| Foreign public corporate securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	1,539,172	906,031
Gross Unrealized Gains	2,455	34,234
Gross Unrealized Losses	163,384	10,363
Allowance for Credit Losses	21	0
Fair Value	1,378,222	929,902
Fixed maturities \| Foreign private corporate securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	4,338,585	2,741,449
Gross Unrealized Gains	19,761	62,932
Gross Unrealized Losses	589,153	48,381
Allowance for Credit Losses	2,863	2,089
Fair Value	3,766,330	2,753,911
Fixed maturities \| Asset-backed securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	1,467,955	547,549
Gross Unrealized Gains	6,976	860
Gross Unrealized Losses	32,577	1,099
Allowance for Credit Losses	0	0
Fair Value	1,442,354	547,310
Fixed maturities \| Commercial mortgage-backed securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	727,159	552,653
Gross Unrealized Gains	94	25,928
Gross Unrealized Losses	69,101	3,397
Allowance for Credit Losses	0	0
Fair Value	658,152	575,184
Fixed maturities \| Residential mortgage-backed securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	342,493	18,684
Gross Unrealized Gains	3,211	1,501
Gross Unrealized Losses	9,479	5
Allowance for Credit Losses	9	0
Fair Value	$ 336,216	$ 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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