AOCI - Reclassification out of Accumulated Other Comprehensive Income (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Reclassification Out of Accumulated Other Comprehensive Income [Line Items]
Fuel and oil	$ 1,015	$ 1,018
Interest Expense	(31)	(32)
Less: Tax Expense	(117)	$ (139)
Interest rate derivatives
Reclassification Out of Accumulated Other Comprehensive Income [Line Items]
Reclassification to earnings	(1)
Reclassification out of Accumulated Other Comprehensive Income
Reclassification Out of Accumulated Other Comprehensive Income [Line Items]
Net of Tax	9
Reclassification out of Accumulated Other Comprehensive Income | Fuel derivatives
Reclassification Out of Accumulated Other Comprehensive Income [Line Items]
Reclassification to earnings	(11)
Less: Tax Expense	3
Net of Tax	8
Reclassification out of Accumulated Other Comprehensive Income | Interest rate derivatives
Reclassification Out of Accumulated Other Comprehensive Income [Line Items]
Net of Tax	$ 1