Financial Derivative Instruments and Risk Management - Net of Tax Impact of the Overall Effectiveness of Derivative Instruments Designated as Cash Flow Hedging Instruments (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Derivative [Line Items]
Derivative contract losses, net of tax impact	$ 1	$ (15)	$ 21
Fuel Derivative Contracts
Derivative [Line Items]
Fuel derivative and interest rate contract gains (losses) - net of tax impact	0	(16)	22
Cash flow hedge reclassification net of tax impact	0	(11)	0
Interest Rate Swap
Derivative [Line Items]
Fuel derivative and interest rate contract gains (losses) - net of tax impact	0	(10)	(1)
Cash flow hedge reclassification net of tax impact	$ 1	$ 0	$ 0