Investments (Amortized Cost and Fair Value of Fixed Maturities by Contractual Maturities) (Details) - USD ($) $ in Thousands	Jun. 30, 2025	Dec. 31, 2024
Amortized Cost
Due in one year or less	$ 2,286,700
Due after one year through five years	15,568,403
Due after five years through ten years	10,149,012
Due after ten years	9,451,585
Amortized Cost	43,550,555	$ 36,980,933
Fair Value
Due in one year or less	2,259,790
Due after one year through five years	15,672,882
Due after five years through ten years	10,232,287
Due after ten years	8,299,535
Fair Value	42,552,406	34,986,160
Asset-backed securities
Amortized Cost
Debt Securities, Available-for-sale, Maturity, without Single Maturity Date, Amortized Cost	4,380,196
Amortized Cost	4,380,196	3,728,073
Fair Value
Debt Securities, Available-for-sale, Maturity, without Single Maturity Date, Fair Value	4,404,426
Fair Value	4,404,426	3,750,663
Commercial mortgage-backed securities
Amortized Cost
Debt Securities, Available-for-sale, Maturity, without Single Maturity Date, Amortized Cost	1,168,631
Amortized Cost	1,168,631	944,652
Fair Value
Debt Securities, Available-for-sale, Maturity, without Single Maturity Date, Fair Value	1,141,171
Fair Value	1,141,171	895,775
Residential mortgage-backed securities
Amortized Cost
Debt Securities, Available-for-sale, Maturity, without Single Maturity Date, Amortized Cost	546,028
Amortized Cost	546,028	367,005
Fair Value
Debt Securities, Available-for-sale, Maturity, without Single Maturity Date, Fair Value	542,315
Fair Value	$ 542,315	$ 356,072