AOCI - Reclassification out of Accumulated Other Comprehensive Income (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Reclassification Out of Accumulated Other Comprehensive Income [Line Items]
Fuel and oil	$ 1,136	$ 1,202	$ 2,152	$ 2,220
Interest Expense	(31)	(33)	(61)	(66)
Less: Tax Expense	(227)	$ (227)	(344)	$ (366)
Interest rate derivatives
Reclassification Out of Accumulated Other Comprehensive Income [Line Items]
Reclassification to earnings	1		2
Reclassification out of Accumulated Other Comprehensive Income
Reclassification Out of Accumulated Other Comprehensive Income [Line Items]
Net of Tax	(1)		9
Reclassification out of Accumulated Other Comprehensive Income | Fuel derivatives
Reclassification Out of Accumulated Other Comprehensive Income [Line Items]
Reclassification to earnings	2		(9)
Less: Tax Expense	0		2
Net of Tax	(2)		7
Reclassification out of Accumulated Other Comprehensive Income | Interest rate derivatives
Reclassification Out of Accumulated Other Comprehensive Income [Line Items]
Less: Tax Expense	0		0
Net of Tax	$ 1		$ 2