Investments (Amortized Cost and Fair Value of Fixed Maturities by Contractual Maturities) (Details) - USD ($) $ in Thousands	Jun. 30, 2023	Dec. 31, 2022
Amortized Cost
Due in one year or less	$ 871,136
Due after one year through five years	7,836,414
Due after five years through ten years	6,286,229
Due after ten years	7,390,491
Amortized Cost	25,557,874	$ 21,311,087
Fair Value
Due in one year or less	851,532
Due after one year through five years	7,422,836
Due after five years through ten years	5,750,612
Due after ten years	6,336,643
Fair Value	23,441,750	$ 19,025,401
Asset-backed securities
Amortized Cost
Debt securities, available-for-sale, maturity, without single maturity date, amortized cost	1,903,744
Fair Value
Debt Securities, Available-for-sale, Maturity, without Single Maturity Date, Fair Value	1,897,566
Commercial mortgage-backed securities
Amortized Cost
Debt securities, available-for-sale, maturity, without single maturity date, amortized cost	858,875
Fair Value
Debt Securities, Available-for-sale, Maturity, without Single Maturity Date, Fair Value	780,105
Residential mortgage-backed securities
Amortized Cost
Debt securities, available-for-sale, maturity, without single maturity date, amortized cost	410,985
Fair Value
Debt Securities, Available-for-sale, Maturity, without Single Maturity Date, Fair Value	$ 402,456

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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