Fair Value Measurements - Narrative (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2022	Mar. 31, 2021	Dec. 31, 2021
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term investments	$ 2,250		$ 3,386
Short-term investments expected to mature in one year or less	1,600
Fuel hedge contracts
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Net losses on fuel hedge contracts	240	$ 57
Loss on settlement	244
Mark-to-market adjustments	$ 4