AOCI - Reclassification out of Accumulated Other Comprehensive Income (Loss) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Reclassification Out of Accumulated Other Comprehensive Income (Loss) [Line Items]
Fuel and oil	$ 379	$ 1,090	$ 1,507	$ 3,242
Other (gains) losses, net	(35)	(3)	(95)	(8)
Less: Tax Expense	385	$ (160)	759	$ (504)
Interest rate derivatives
Reclassification Out of Accumulated Other Comprehensive Income (Loss) [Line Items]
Reclassification to earnings	0		(1)
Reclassification out of Accumulated Other Comprehensive Income (Loss)
Reclassification Out of Accumulated Other Comprehensive Income (Loss) [Line Items]
Net of Tax	31		72
Reclassification out of Accumulated Other Comprehensive Income (Loss) | Fuel derivatives
Reclassification Out of Accumulated Other Comprehensive Income (Loss) [Line Items]
Reclassification to earnings	(40)		(92)
Less: Tax Expense	(9)		(21)
Net of Tax			71
Fuel derivatives | Reclassification out of Accumulated Other Comprehensive Income (Loss)
Reclassification Out of Accumulated Other Comprehensive Income (Loss) [Line Items]
Fuel and oil	18		54
Other (gains) losses, net	$ 22		38
Interest rate derivatives | Reclassification out of Accumulated Other Comprehensive Income (Loss)
Reclassification Out of Accumulated Other Comprehensive Income (Loss) [Line Items]
Less: Tax Expense			0
Net of Tax			$ 1