Comprehensive Income - Reclassification out of Accumulated Other Comprehensive Income (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
Reclassification Out of Accumulated Other Comprehensive Income [Line Items]
Fuel and oil	$ (852)	$ (877)
Interest Expense	(30)	(32)
Less: Tax Expense	305	$ 270
Reclassification out of Accumulated Other Comprehensive Income
Reclassification Out of Accumulated Other Comprehensive Income [Line Items]
Net of Tax	197
Fuel derivatives | Reclassification out of Accumulated Other Comprehensive Income
Reclassification Out of Accumulated Other Comprehensive Income [Line Items]
Fuel and oil	310
Less: Tax Expense	115
Net of Tax	195
Interest rate derivatives | Reclassification out of Accumulated Other Comprehensive Income
Reclassification Out of Accumulated Other Comprehensive Income [Line Items]
Interest Expense	4
Less: Tax Expense	2
Net of Tax	$ 2