Comprehensive Income - Reclassification out of Accumulated Other Comprehensive Income (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Reclassification Out of Accumulated Other Comprehensive Income [Line Items]
Fuel and oil	$ (1,450)	$ (1,528)	$ (4,396)	$ (4,615)
Less: Tax Expense	160	17	334	217
Reclassification out of Accumulated Other Comprehensive Income [Member]
Reclassification Out of Accumulated Other Comprehensive Income [Line Items]
Net of Tax	28		102
Fuel derivatives | Reclassification out of Accumulated Other Comprehensive Income [Member]
Reclassification Out of Accumulated Other Comprehensive Income [Line Items]
Fuel and oil	37		140
Less: Tax Expense	13		52
Net of Tax	24		88
Interest rate derivatives | Reclassification out of Accumulated Other Comprehensive Income [Member]
Reclassification Out of Accumulated Other Comprehensive Income [Line Items]
Interest Expense	7		22
Less: Tax Expense	3		8
Net of Tax	$ 4		$ 14