Fixed Maturity Securities In An Unrealized Loss Position (Securities in an Unrealized Loss Position) (Details) - USD ($) $ in Thousands	Mar. 31, 2023	Dec. 31, 2022
Debt securities
Debt Securities, Available-for-sale [Line Items]
Fair Value, Less than 12 Months	$ 5,900,583	$ 8,843,558
Gross Unrealized Losses, Less than 12 Months	167,885	403,241
Fair Value, 12 Months or Greater	8,855,480	6,763,340
Gross Unrealized Losses, 12 Months or Greater	748,768	719,593
Fair Value, Total	14,756,063	15,606,898
Gross Unrealized Losses, Total	916,653	1,122,834
U.S. government and government agency
Debt Securities, Available-for-sale [Line Items]
Fair Value, Less than 12 Months	213,369	285,391
Gross Unrealized Losses, Less than 12 Months	4,312	10,219
Fair Value, 12 Months or Greater	527,765	453,520
Gross Unrealized Losses, 12 Months or Greater	50,353	58,939
Fair Value, Total	741,134	738,911
Gross Unrealized Losses, Total	54,665	69,158
State and municipal
Debt Securities, Available-for-sale [Line Items]
Fair Value, Less than 12 Months	1,070,807	1,720,443
Gross Unrealized Losses, Less than 12 Months	30,908	89,272
Fair Value, 12 Months or Greater	1,008,985	598,797
Gross Unrealized Losses, 12 Months or Greater	96,512	79,320
Fair Value, Total	2,079,792	2,319,240
Gross Unrealized Losses, Total	127,420	168,592
Mortgage-backed
Debt Securities, Available-for-sale [Line Items]
Fair Value, Less than 12 Months	765,967	1,099,549
Gross Unrealized Losses, Less than 12 Months	17,720	75,430
Fair Value, 12 Months or Greater	866,618	473,318
Gross Unrealized Losses, 12 Months or Greater	148,720	115,528
Fair Value, Total	1,632,585	1,572,867
Gross Unrealized Losses, Total	166,440	190,958
Asset-backed
Debt Securities, Available-for-sale [Line Items]
Fair Value, Less than 12 Months	916,431	1,569,647
Gross Unrealized Losses, Less than 12 Months	13,102	48,390
Fair Value, 12 Months or Greater	2,490,520	2,176,638
Gross Unrealized Losses, 12 Months or Greater	104,751	103,932
Fair Value, Total	3,406,951	3,746,285
Gross Unrealized Losses, Total	117,853	152,322
Corporate
Debt Securities, Available-for-sale [Line Items]
Fair Value, Less than 12 Months	2,694,062	3,690,856
Gross Unrealized Losses, Less than 12 Months	75,595	150,115
Fair Value, 12 Months or Greater	3,175,233	2,349,281
Gross Unrealized Losses, 12 Months or Greater	264,845	256,631
Fair Value, Total	5,869,295	6,040,137
Gross Unrealized Losses, Total	340,440	406,746
Foreign government
Debt Securities, Available-for-sale [Line Items]
Fair Value, Less than 12 Months	239,947	477,672
Gross Unrealized Losses, Less than 12 Months	26,248	29,815
Fair Value, 12 Months or Greater	786,359	711,786
Gross Unrealized Losses, 12 Months or Greater	83,587	105,243
Fair Value, Total	1,026,306	1,189,458
Gross Unrealized Losses, Total	$ 109,835	$ 135,058

Amount of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), in continuous unrealized loss position for more than 12 months, without allowance for credit loss. Includes beneficial interest in securitized financial asset.

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-Name Accounting Standards Codification
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-SubTopic 30
-Section 50
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Amount of accumulated unrealized loss on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), in continuous unrealized loss position for 12 months or longer, without allowance for credit loss. Includes beneficial interest in securitized financial asset.

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Amount of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), in continuous unrealized loss position for less than 12 months, without allowance for credit loss. Includes beneficial interest in securitized financial asset.

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Amount of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), in unrealized loss position without allowance for credit loss.

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Amount of accumulated unrealized loss on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), in unrealized loss position, without allowance for credit loss. Includes beneficial interest in securitized financial asset.

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Amount of accumulated unrealized loss on investment in debt security measured at amortized cost (held-to-maturity), in continuous loss position for less than 12 months.

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