Comprehensive Income - Reclassification out of Accumulated Other Comprehensive Income (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Reclassification Out of Accumulated Other Comprehensive Income [Line Items]
Fuel and oil	$ (922)	$ (852)
Interest Expense	(29)	(30)
Less: Tax Expense	202	$ 303
Reclassification out of Accumulated Other Comprehensive Income
Reclassification Out of Accumulated Other Comprehensive Income [Line Items]
Net of Tax	90
Fuel derivatives | Reclassification out of Accumulated Other Comprehensive Income
Reclassification Out of Accumulated Other Comprehensive Income [Line Items]
Fuel and oil	139
Less: Tax Expense	51
Net of Tax	88
Interest rate derivatives | Reclassification out of Accumulated Other Comprehensive Income
Reclassification Out of Accumulated Other Comprehensive Income [Line Items]
Interest Expense	3
Less: Tax Expense	1
Net of Tax	$ 2