Comprehensive Income - Reclassification out of Accumulated Other Comprehensive Income (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Reclassification Out of Accumulated Other Comprehensive Income [Line Items]
Fuel and oil	$ (903)	$ (1,005)	$ (1,755)	$ (1,882)
Interest Expense	(32)	(29)	(62)	(62)
Less: Tax Expense	484	$ 369	787	$ 638
Reclassification out of Accumulated Other Comprehensive Income
Reclassification Out of Accumulated Other Comprehensive Income [Line Items]
Net of Tax	152		349
Fuel derivatives | Reclassification out of Accumulated Other Comprehensive Income
Reclassification Out of Accumulated Other Comprehensive Income [Line Items]
Fuel and oil	236		546
Less: Tax Expense	87		202
Net of Tax	149		344
Interest rate derivatives | Reclassification out of Accumulated Other Comprehensive Income
Reclassification Out of Accumulated Other Comprehensive Income [Line Items]
Interest Expense	4		8
Less: Tax Expense	1		3
Net of Tax	$ 3		$ 5