Financial Derivative Instruments - Offsetting Derivative Liabilities (Details) - USD ($) $ in Millions	Dec. 31, 2022	Dec. 31, 2021
Fuel derivative contracts | Prepaid expenses and other current assets
Offsetting Liabilities
Gross amounts offset in the balance sheet	$ 106	$ 80
Gross amounts offset in the Balance Sheet	(106)	(80)
Net amounts of liabilities presented in the Balance Sheet	$ 0	$ 0
Derivative Liability, Statement of Financial Position [Extensible Enumeration]	Prepaid expenses and other current assets	Prepaid expenses and other current assets
Fuel derivative contracts | Other assets
Offsetting Liabilities
Gross amounts offset in the balance sheet	$ 0	$ 95
Gross amounts offset in the Balance Sheet	0	(95)
Net amounts of liabilities presented in the Balance Sheet	$ 0	$ 0
Derivative Liability, Statement of Financial Position [Extensible Enumeration]	Other assets	Other assets
Interest rate derivatives
Offsetting Liabilities
Net amounts of liabilities presented in the Balance Sheet	$ 0	$ 4
Interest rate derivatives | Other noncurrent liabilities
Offsetting Liabilities
Gross amounts offset in the balance sheet	0	4
Gross amounts offset in the Balance Sheet	$ 0	$ 0
Derivative Liability, Statement of Financial Position [Extensible Enumeration]	Other noncurrent liabilities	Other noncurrent liabilities