Fair Value Measurements - Schedule of Fair Value of Investment Assets (Details) - Fair Value - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total investments at fair value	$ 1,084	$ 341
Level 2
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total investments at fair value	1,084	341
Level 2 | Certificates of Deposit and Commercial Paper
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total investments at fair value	989	250
Level 2 | Corporate Bonds
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total investments at fair value	59	56
Level 2 | Government Securities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total investments at fair value	$ 36	$ 35