Financial Derivative Instruments - Offsetting Derivative Liabilities (Details) - USD ($) $ in Millions	Jun. 30, 2022	Dec. 31, 2021
Offsetting Liabilities [Line Items]
Gross amounts of recognized liabilities	$ 167	$ 4
Fuel derivative contracts | Prepaid expenses and other current assets
Offsetting Liabilities [Line Items]
Gross amounts of recognized liabilities	464	80
Gross amounts offset in the Balance Sheet	(464)	(80)
Net amounts of liabilities presented in the Balance Sheet	0	0
Fuel derivative contracts | Other assets
Offsetting Liabilities [Line Items]
Gross amounts of recognized liabilities	162	95
Gross amounts offset in the Balance Sheet	(162)	(95)
Net amounts of liabilities presented in the Balance Sheet	0	0
Interest rate derivative contracts | Other noncurrent liabilities
Offsetting Liabilities [Line Items]
Gross amounts of recognized liabilities	0	4
Gross amounts offset in the Balance Sheet	0	0
Net amounts of liabilities presented in the Balance Sheet	$ 0	$ 4