Investments (Amortized Cost and Fair Value of Fixed Maturities by Contractual Maturities) (Details) - USD ($) $ in Thousands	Dec. 31, 2024	Dec. 31, 2023
Amortized Cost
Due in one year or less	$ 1,139,538
Due after one year through five years	11,753,438
Due after five years through ten years	10,291,196
Due after ten years	8,757,031
Amortized Cost	36,980,933	$ 27,538,066
Fair Value
Due in one year or less	1,118,484
Due after one year through five years	11,477,710
Due after five years through ten years	9,883,263
Due after ten years	7,504,193
Fair Value	34,986,160	26,131,780
Asset-backed securities
Amortized Cost
Debt Securities, Available-for-sale,Maturity, without Single Maturity Date,Amortized Cost	3,728,073
Amortized Cost	3,728,073	2,016,028
Fair Value
Debt Securities, Available-for-sale,Maturity, without Single Maturity Date,Fair Value	3,750,663
Fair Value	3,750,663	2,027,550
Commercial mortgage-backed securities
Amortized Cost
Debt Securities, Available-for-sale,Maturity, without Single Maturity Date,Amortized Cost	944,652
Amortized Cost	944,652	913,347
Fair Value
Debt Securities, Available-for-sale,Maturity, without Single Maturity Date,Fair Value	895,775
Fair Value	895,775	851,778
Residential mortgage-backed securities
Amortized Cost
Debt Securities, Available-for-sale,Maturity, without Single Maturity Date,Amortized Cost	367,005
Amortized Cost	367,005	399,542
Fair Value
Debt Securities, Available-for-sale,Maturity, without Single Maturity Date,Fair Value	356,072
Fair Value	$ 356,072	$ 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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