Investment Information - Maturity profile of available for sale securities (Details) - USD ($) $ in Thousands	Dec. 31, 2022	Dec. 31, 2021
Estimated Fair Value:
Estimated fair value	$ 21,014,451	$ 19,732,825
Amortized Cost:
Amortized cost	22,614,859	19,708,561
Fixed maturities available for sale, at fair value
Estimated Fair Value:
Due in one year or less	510,669	300,889
Due after one year through five years	11,014,753	8,355,255
Due after five years through 10 years	3,984,497	4,689,155
Due after 10 years	403,387	505,758
Single maturity date	15,913,306	13,851,057
Estimated fair value	19,682,789	17,998,109
Amortized Cost:
Due in one year or less	536,962	299,772
Due after one year through five years	11,714,427	8,339,387
Due after five years through 10 years	4,527,447	4,684,393
Due after 10 years	479,546	493,927
Single maturity date	17,258,382	13,817,479
Amortized cost	21,281,863	17,973,823
Fixed maturities available for sale, at fair value | Mortgage backed securities
Estimated Fair Value:
Securities without single maturity date	795,391	408,477
Estimated fair value	795,391	408,477
Amortized Cost:
Securities without single maturity date	877,043	411,110
Amortized cost	877,043	411,110
Fixed maturities available for sale, at fair value | Commercial mortgage backed securities
Estimated Fair Value:
Securities without single maturity date	1,047,275	1,046,484
Estimated fair value	1,047,275	1,046,484
Amortized Cost:
Securities without single maturity date	1,107,749	1,047,867
Amortized cost	1,107,749	1,047,867
Fixed maturities available for sale, at fair value | Asset backed securities
Estimated Fair Value:
Securities without single maturity date	1,926,817	2,692,091
Estimated fair value	1,926,817	2,692,091
Amortized Cost:
Securities without single maturity date	2,038,689	2,697,367
Amortized cost	$ 2,038,689	$ 2,697,367