Financial Derivative Instruments - Offsetting of Derivative Assets (Details) - USD ($) $ in Millions	Mar. 31, 2024	Dec. 31, 2023
Offsetting Assets [Line Items]
Gross amounts of recognized assets	$ 280	$ 223
Fuel derivative contracts | Prepaid expenses and other current assets
Offsetting Assets [Line Items]
Gross amounts of recognized assets	132	86
Gross amounts offset in the Balance Sheet	(41)	(15)
Net amounts of assets presented in the Balance Sheet	$ 91	$ 71
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	$ 148	$ 137
Gross amounts offset in the Balance Sheet	(32)	(35)
Net amounts of assets presented in the Balance Sheet	$ 116	$ 102
Derivative Asset, Statement of Financial Position [Extensible Enumeration]	Other assets	Other assets