Fair Value Measurements - Schedule of Fair Value of Investment Assets (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Fair Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total investments at fair value	$ 101	$ 1,084
Carrying Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total investments at amortized cost	89	1,076
Level 2 | Fair Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total investments at fair value	101	1,084
Level 2 | Fair Value | Corporate Bonds
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total investments at fair value	68	59
Level 2 | Fair Value | Government Securities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total investments at fair value	33	36
Level 2 | Fair Value | Commercial Paper and Certificates of Deposit
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total investments at fair value	$ 0	$ 989