Investments (Amortized Cost and Fair Value of Fixed Maturities by Contractual Maturities) (Details) - USD ($) $ in Thousands	Jun. 30, 2024	Dec. 31, 2023
Amortized Cost
Due in one year or less	$ 1,585,826
Due after one year through five years	10,560,134
Due after five years through ten years	8,207,957
Due after ten years	8,085,252
Amortized Cost	33,149,962	$ 27,538,066
Fair Value
Due in one year or less	1,549,703
Due after one year through five years	10,212,123
Due after five years through ten years	7,798,270
Due after ten years	6,891,565
Fair Value	31,110,763	26,131,780
Asset-backed securities
Amortized Cost
Debt securities, available-for-sale, maturity, without single maturity date, amortized cost	3,403,884
Amortized Cost	3,403,884	2,016,028
Fair Value
Debt Securities, Available-for-sale, Maturity, without Single Maturity Date, Fair Value	3,427,269
Fair Value	3,427,269	2,027,550
Commercial mortgage-backed securities
Amortized Cost
Debt securities, available-for-sale, maturity, without single maturity date, amortized cost	922,301
Amortized Cost	922,301	913,347
Fair Value
Debt Securities, Available-for-sale, Maturity, without Single Maturity Date, Fair Value	859,062
Fair Value	859,062	851,778
Residential mortgage-backed securities
Amortized Cost
Debt securities, available-for-sale, maturity, without single maturity date, amortized cost	384,608
Amortized Cost	384,608	399,542
Fair Value
Debt Securities, Available-for-sale, Maturity, without Single Maturity Date, Fair Value	372,771
Fair Value	$ 372,771	$ 396,070

Amortized cost 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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