Comprehensive Income - Reclassification out of Accumulated Other Comprehensive Income (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013
Reclassification Out of Accumulated Other Comprehensive Income [Line Items]
Fuel and oil	$ (1,425)	$ (1,489)	$ (2,739)	$ (2,946)
Less: Tax Expense	281	139	373	173
Reclassification out of Accumulated Other Comprehensive Income [Member]
Reclassification Out of Accumulated Other Comprehensive Income [Line Items]
Net of Tax	2		6
Fuel derivatives | Reclassification out of Accumulated Other Comprehensive Income [Member]
Reclassification Out of Accumulated Other Comprehensive Income [Line Items]
Fuel and oil	(2)		(2)
Less: Tax Expense	(1)		(1)
Net of Tax	(1)		(1)
Interest rate derivatives | Reclassification out of Accumulated Other Comprehensive Income [Member]
Reclassification Out of Accumulated Other Comprehensive Income [Line Items]
Interest Expense	5		11
Less: Tax Expense	2		4
Net of Tax	$ 3		$ 7