Investments (Amortized Cost and Fair Value of Fixed Maturities by Contractual Maturities) (Details) - USD ($) $ in Thousands	Sep. 30, 2024	Dec. 31, 2023
Amortized Cost
Due in one year or less	$ 1,451,746
Due after one year through five years	11,583,221
Due after five years through ten years	9,102,232
Due after ten years	8,800,517
Amortized Cost	35,694,374	$ 27,538,066
Fair Value
Due in one year or less	1,437,659
Due after one year through five years	11,565,272
Due after five years through ten years	9,116,421
Due after ten years	8,074,424
Fair Value	34,956,806	26,131,780
Asset-backed securities
Amortized Cost
Debt securities, available-for-sale, maturity, without single maturity date, amortized cost	3,450,724
Amortized Cost	3,450,724	2,016,028
Fair Value
Debt Securities, Available-for-sale, Maturity, without Single Maturity Date, Fair Value	3,490,040
Fair Value	3,490,040	2,027,550
Commercial mortgage-backed securities
Amortized Cost
Debt securities, available-for-sale, maturity, without single maturity date, amortized cost	929,684
Amortized Cost	929,684	913,347
Fair Value
Debt Securities, Available-for-sale, Maturity, without Single Maturity Date, Fair Value	895,436
Fair Value	895,436	851,778
Residential mortgage-backed securities
Amortized Cost
Debt securities, available-for-sale, maturity, without single maturity date, amortized cost	376,250
Amortized Cost	376,250	399,542
Fair Value
Debt Securities, Available-for-sale, Maturity, without Single Maturity Date, Fair Value	377,554
Fair Value	$ 377,554	$ 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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