Investments (Amortized Cost and Fair Value of Fixed Maturities by Contractual Maturities) (Details) - USD ($) $ in Thousands	Sep. 30, 2022	Dec. 31, 2021
Amortized Cost
Due in one year or less	$ 368,359
Due after one year through five years	4,518,851
Due after five years through ten years	5,618,197
Due after ten years	6,434,977
Amortized Cost	19,108,100	$ 12,737,749
Fair Value
Due in one year or less	353,441
Due after one year through five years	4,099,378
Due after five years through ten years	4,741,344
Due after ten years	5,086,315
Fair Value	16,321,510	13,278,166
Asset-backed securities
Amortized Cost
Debt Securities, Available-for-sale, Maturity, without Single Maturity Date, Amortized Cost	1,296,006
Fair Value
Debt Securities, Available-for-sale, Maturity, without Single Maturity Date, Fair Value	1,252,154
Commercial mortgage-backed securities
Amortized Cost
Debt Securities, Available-for-sale, Maturity, without Single Maturity Date, Amortized Cost	726,470
Fair Value
Debt Securities, Available-for-sale, Maturity, without Single Maturity Date, Fair Value	653,339
Residential mortgage-backed securities
Amortized Cost
Debt Securities, Available-for-sale, Maturity, without Single Maturity Date, Amortized Cost	145,240
Fair Value
Debt Securities, Available-for-sale, Maturity, without Single Maturity Date, Fair Value	135,539
Fixed maturities
Amortized Cost
Amortized Cost	19,108,100	12,737,749
Fair Value
Fair Value	16,321,510	13,278,166
Fixed maturities \| Asset-backed securities
Amortized Cost
Amortized Cost	1,296,006	547,549
Fair Value
Fair Value	1,252,154	547,310
Fixed maturities \| Commercial mortgage-backed securities
Amortized Cost
Amortized Cost	726,470	552,653
Fair Value
Fair Value	653,339	575,184
Fixed maturities \| Residential mortgage-backed securities
Amortized Cost
Amortized Cost	145,240	18,684
Fair Value
Fair Value	$ 135,539	$ 20,180

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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