Comprehensive Income - Reclassification out of Accumulated Other Comprehensive Income (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Reclassification Out of Accumulated Other Comprehensive Income [Line Items]
Fuel and oil	$ (1,386)	$ (1,450)	$ (4,125)	$ (4,396)
Less: Tax Expense	196	160	569	334
Reclassification out of Accumulated Other Comprehensive Income [Member]
Reclassification Out of Accumulated Other Comprehensive Income [Line Items]
Net of Tax	8		13
Fuel derivatives | Reclassification out of Accumulated Other Comprehensive Income [Member]
Reclassification Out of Accumulated Other Comprehensive Income [Line Items]
Fuel and oil	6		4
Less: Tax Expense	2		1
Net of Tax	4		3
Interest rate derivatives | Reclassification out of Accumulated Other Comprehensive Income [Member]
Reclassification Out of Accumulated Other Comprehensive Income [Line Items]
Interest Expense	6		17
Less: Tax Expense	2		7
Net of Tax	$ 4		$ 10