Investments - Estimated fair values of short and long-term investments classified by date of contractual maturity (Details) - USD ($) $ in Millions	Jun. 30, 2023	Dec. 31, 2022
Debt Securities, Available-for-sale [Line Items]
One year or less (including restricted cash of $22)	$ 2,111
One year through two years (including restricted cash of $4)	645
Two years through three years	227
Three years through four years	72
Estimated Fair Value	3,055
Short-term investments:
Debt Securities, Available-for-sale [Line Items]
Restricted cash included in long-term investments	2,123	$ 2,532
Estimated Fair Value	2,111	2,521
Short-term investments: | Restricted cash
Debt Securities, Available-for-sale [Line Items]
Restricted cash included in long-term investments	22	36
Estimated Fair Value	22	36
Long-term investments:
Debt Securities, Available-for-sale [Line Items]
Restricted cash included in long-term investments	1,011	1,303
Estimated Fair Value	944	1,216
Long-term investments: | Restricted cash
Debt Securities, Available-for-sale [Line Items]
Restricted cash included in long-term investments	4	13
Estimated Fair Value	$ 4	$ 13