Investments (Fixed Maturities Securities Excluding Investments Classified as Trading) (Details) - USD ($) $ in Thousands	Sep. 30, 2022	Dec. 31, 2021
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	$ 19,108,100	$ 12,737,749
Allowance for Credit Losses	4,712	4,149
Fair Value	16,321,510	13,278,166
Fixed maturities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	19,108,100	12,737,749
Gross Unrealized Gain	26,389	658,544
Gross Unrealized Losses	2,808,267	113,978
Allowance for Credit Losses	4,712	4,149
Fair Value	16,321,510	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	304,752	303,040
Gross Unrealized Gain	336	31,011
Gross Unrealized Losses	69,382	111
Allowance for Credit Losses	0	0
Fair Value	235,706	333,940
Fixed maturities \| Obligations of U.S. states and their political subdivisions
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	612,918	584,244
Gross Unrealized Gain	1,729	46,978
Gross Unrealized Losses	49,593	701
Allowance for Credit Losses	0	0
Fair Value	565,054	630,521
Fixed maturities \| Foreign government bonds
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	331,252	324,454
Gross Unrealized Gain	865	29,299
Gross Unrealized Losses	72,507	3,271
Allowance for Credit Losses	10	11
Fair Value	259,600	350,471
Fixed maturities \| U.S. public corporate securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	7,004,770	4,794,878
Gross Unrealized Gain	13,841	366,764
Gross Unrealized Losses	1,127,789	29,770
Allowance for Credit Losses	0	0
Fair Value	5,890,822	5,131,872
Fixed maturities \| U.S. private corporate securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	3,572,279	1,964,767
Gross Unrealized Gain	7,959	59,037
Gross Unrealized Losses	379,408	16,880
Allowance for Credit Losses	1,342	2,049
Fair Value	3,199,488	2,004,875
Fixed maturities \| Foreign public corporate securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	1,471,519	906,031
Gross Unrealized Gain	1,098	34,234
Gross Unrealized Losses	195,069	10,363
Allowance for Credit Losses	490	0
Fair Value	1,277,058	929,902
Fixed maturities \| Foreign private corporate securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	3,642,894	2,741,449
Gross Unrealized Gain	25	62,932
Gross Unrealized Losses	787,306	48,381
Allowance for Credit Losses	2,863	2,089
Fair Value	2,852,750	2,753,911
Fixed maturities \| Asset-backed securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	1,296,006	547,549
Gross Unrealized Gain	309	860
Gross Unrealized Losses	44,161	1,099
Allowance for Credit Losses	0	0
Fair Value	1,252,154	547,310
Fixed maturities \| Commercial mortgage-backed securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	726,470	552,653
Gross Unrealized Gain	0	25,928
Gross Unrealized Losses	73,131	3,397
Allowance for Credit Losses	0	0
Fair Value	653,339	575,184
Fixed maturities \| Residential mortgage-backed securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	145,240	18,684
Gross Unrealized Gain	227	1,501
Gross Unrealized Losses	9,921	5
Allowance for Credit Losses	7	0
Fair Value	$ 135,539	$ 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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