Financial Derivative Instruments - Offsetting of Derivative Assets (Details) - USD ($) $ in Millions	Jun. 30, 2023	Dec. 31, 2022
Offsetting Assets [Line Items]
Gross amounts of recognized assets	$ 353	$ 526
Fuel derivative contracts | Prepaid expenses and other current assets
Offsetting Assets [Line Items]
Gross amounts of recognized assets	145	352
Gross amounts offset in the Balance Sheet	(50)	(106)
Net amounts of assets presented in the Balance Sheet	$ 95	$ 246
Derivative Asset, Statement of Financial Position [Extensible Enumeration]	Prepaid expenses and other current assets	Prepaid expenses and other current assets
Fuel derivative contracts | Other assets
Offsetting Assets [Line Items]
Gross amounts of recognized assets	$ 194	$ 160
Gross amounts offset in the Balance Sheet	(33)	0
Net amounts of assets presented in the Balance Sheet	$ 161	$ 160
Derivative Asset, Statement of Financial Position [Extensible Enumeration]	Other assets	Other assets
Interest rate derivative contracts
Offsetting Assets [Line Items]
Net amounts of assets presented in the Balance Sheet	$ 14	$ 14
Interest rate derivative contracts | Other assets
Offsetting Assets [Line Items]
Gross amounts of recognized assets	14	14
Gross amounts offset in the Balance Sheet	$ 0	$ 0
Derivative Asset, Statement of Financial Position [Extensible Enumeration]	Other assets	Other assets