Investments (Contractual maturity) (Details) - USD ($) $ in Millions	Jun. 30, 2024	Dec. 31, 2023
Investments [Abstract]
Due in one year or less, cost or amortized cost	$ 1,528	$ 1,121
Due after one year through five years, cost or amortized cost	11,521	11,563
Due after five years through ten years, cost or amortized cost	13,115	13,359
Due after ten years, cost or amortized cost	16,825	16,371
Cost or Amortized Cost	42,989	42,414
Due in one year or less, estimated fair value	1,493	1,091
Due after one year through five years, estimated fair value	11,129	11,180
Due after five years through ten years, estimated fair value	12,225	12,573
Due after ten years, estimated fair value	15,552	15,581
Estimated Fair Value	$ 40,399	$ 40,425