Comprehensive Income - Reclassification out of Accumulated Other Comprehensive Income (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Reclassification Out of Accumulated Other Comprehensive Income [Line Items]
Fuel and oil	$ (1,005)	$ (1,425)	$ (1,882)	$ (2,739)
Less: Tax Expense	369	$ 281	638	$ 373
Reclassification out of Accumulated Other Comprehensive Income [Member]
Reclassification Out of Accumulated Other Comprehensive Income [Line Items]
Net of Tax	44		93
Fuel derivatives | Reclassification out of Accumulated Other Comprehensive Income [Member]
Reclassification Out of Accumulated Other Comprehensive Income [Line Items]
Fuel and oil	65		138
Less: Tax Expense	24		51
Net of Tax	41		87
Interest rate derivatives | Reclassification out of Accumulated Other Comprehensive Income [Member]
Reclassification Out of Accumulated Other Comprehensive Income [Line Items]
Interest Expense	5		10
Less: Tax Expense	2		4
Net of Tax	$ 3		$ 6