Investments (Contractual maturity) (Details) - USD ($) $ in Millions	Sep. 30, 2025	Dec. 31, 2024
Investments [Abstract]
Due in one year or less, cost or amortized cost	$ 1,275	$ 1,761
Due after one year through five years, cost or amortized cost	11,741	11,678
Due after five years through ten years, cost or amortized cost	13,010	13,134
Due after ten years, cost or amortized cost	18,883	16,908
Cost or Amortized Cost	44,909	43,481
Due in one year or less, estimated fair value	1,267	1,753
Due after one year through five years, estimated fair value	11,578	11,403
Due after five years through ten years, estimated fair value	12,764	12,415
Due after ten years, estimated fair value	18,078	15,540
Estimated Fair Value	$ 43,687	$ 41,111