Fair Value Measurements - Assets and Liabilities Measured at Fair Value on a Recurring Basis (Details) - Fair Value - USD ($) $ in Millions	Jun. 30, 2021	Dec. 31, 2020
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term investments	$ 1,963	$ 2,164
Net derivative contracts	(44)	(179)
Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term investments	1,755	1,603
Net derivative contracts	0	0
Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term investments	208	561
Net derivative contracts	(44)	(179)
Total Cost Basis
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term investments	1,963	2,164
Net derivative contracts	$ 0	$ 0