Investment Information - Maturity profile of available for sale securities) (Details) - USD ($) $ in Thousands	Jun. 30, 2022	Dec. 31, 2021
Estimated Fair Value
Estimated Fair Value	$ 19,812,903	$ 19,732,825
Amortized Cost
Cost or Amortized Cost	21,043,045	19,708,561
Fixed maturities
Estimated Fair Value
Due in one year or less	412,194	300,889
Due after one year through five years	9,423,547	8,355,255
Due after five years through 10 years	4,070,099	4,689,155
Due after 10 years	350,188	505,758
Single maturity date	14,256,028	13,851,057
Estimated Fair Value	17,585,029	17,998,109
Amortized Cost
Due in one year or less	414,752	299,772
Due after one year through five years	9,927,876	8,339,387
Due after five years through 10 years	4,512,685	4,684,393
Due after 10 years	442,515	493,927
Single maturity date	15,297,828	13,817,479
Cost or Amortized Cost	18,816,372	17,973,823
Fixed maturities | Mortgage backed securities
Estimated Fair Value
Securities without single maturity date	698,168	408,477
Estimated Fair Value	698,168	408,477
Amortized Cost
Securities without single maturity date	749,639	411,110
Cost or Amortized Cost	749,639	411,110
Fixed maturities | Commercial mortgage backed securities
Estimated Fair Value
Securities without single maturity date	1,023,088	1,046,484
Estimated Fair Value	1,023,088	1,046,484
Amortized Cost
Securities without single maturity date	1,067,205	1,047,867
Cost or Amortized Cost	1,067,205	1,047,867
Fixed maturities | Asset backed securities
Estimated Fair Value
Securities without single maturity date	1,607,745	2,692,091
Estimated Fair Value	1,607,745	2,692,091
Amortized Cost
Securities without single maturity date	1,701,700	2,697,367
Cost or Amortized Cost	$ 1,701,700	$ 2,697,367