Investments (Amortized Cost and Fair Value of Fixed Maturities by Contractual Maturities) (Details) - USD ($) $ in Thousands	Mar. 31, 2025	Dec. 31, 2024
Amortized Cost
Due in one year or less	$ 2,712,978
Due after one year through five years	14,221,040
Due after five years through ten years	9,501,783
Due after ten years	9,193,006
Amortized Cost	40,807,986	$ 36,980,933
Fair Value
Due in one year or less	2,661,173
Due after one year through five years	14,064,348
Due after five years through ten years	9,267,750
Due after ten years	8,020,759
Fair Value	39,166,072	34,986,160
Asset-backed securities
Amortized Cost
Debt Securities, Available-for-sale, Maturity, without Single Maturity Date, Amortized Cost	3,801,789
Amortized Cost	3,801,789	3,728,073
Fair Value
Debt Securities, Available-for-sale, Maturity, without Single Maturity Date, Fair Value	3,816,356
Fair Value	3,816,356	3,750,663
Commercial mortgage-backed securities
Amortized Cost
Debt Securities, Available-for-sale, Maturity, without Single Maturity Date, Amortized Cost	1,018,053
Amortized Cost	1,018,053	944,652
Fair Value
Debt Securities, Available-for-sale, Maturity, without Single Maturity Date, Fair Value	981,540
Fair Value	981,540	895,775
Residential mortgage-backed securities
Amortized Cost
Debt Securities, Available-for-sale, Maturity, without Single Maturity Date, Amortized Cost	359,337
Amortized Cost	359,337	367,005
Fair Value
Debt Securities, Available-for-sale, Maturity, without Single Maturity Date, Fair Value	354,146
Fair Value	$ 354,146	$ 356,072

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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