Investments (Contractual maturity) (Details) - USD ($) $ in Millions	Mar. 31, 2023	Dec. 31, 2022
Investments [Abstract]
Due in one year or less, cost or amortized cost	$ 1,009	$ 1,012
Due after one year through five years, cost or amortized cost	10,486	9,880
Due after five years through ten years, cost or amortized cost	13,763	13,788
Due after ten years, cost or amortized cost	16,388	16,352
Cost or Amortized Cost	41,646	41,032
Due in one year or less, estimated fair value	989	1,001
Due after one year through five years, estimated fair value	10,035	9,399
Due after five years through ten years, estimated fair value	12,702	12,453
Due after ten years, estimated fair value	15,367	14,774
Estimated Fair Value	$ 39,093	$ 37,627