Investments - Contractual Maturity (Details) - USD ($) $ in Millions	Dec. 31, 2021	Dec. 31, 2020
Investments, Debt and Equity Securities [Abstract]
One year or less (including restricted cash of $22)	$ 4,199
One year through two years	442
Two years through three years	752
Three years through four years	391
Four years through five years	124
Thereafter	18
Estimated Fair Value	5,926
Restricted cash included in short-term investments	$ 22	$ 137