Investments in debt and equity securities - Cost basis and fair value of the available-for-sale debt securities by contractual maturity (Details) - USD ($) $ in Millions	Dec. 31, 2023	Dec. 31, 2022
Cost Basis
Due in one year or less	$ 970
Due after one year through five years	1,996
Due after five years through ten years	253
Due after ten years	79
Cost Basis	3,871	$ 3,311
Fair Value
Due in one year or less	963
Due after one year through five years	1,966
Due after five years through ten years	249
Due after ten years	79
Fair Value	3,797	3,164
U.S. governmental agency
Cost Basis
Cost Basis	433	364
Fair Value
Fair Value	410	333
Residential
Cost Basis
Cost Basis	3	3
Fair Value
Fair Value	2	2
Commercial
Cost Basis
Cost Basis	137	127
Fair Value
Fair Value	$ 128	$ 117