Comprehensive Income - Reclassification out of Accumulated Other Comprehensive Income (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
Reclassification Out of Accumulated Other Comprehensive Income [Line Items]
Fuel and oil	$ (1,489)	$ (1,577)	$ (2,946)	$ (3,087)
Less: Tax Expense	139	140	173	200
Reclassification out of Accumulated Other Comprehensive Income [Member]
Reclassification Out of Accumulated Other Comprehensive Income [Line Items]
Net of Tax	41		72
Fuel derivatives | Reclassification out of Accumulated Other Comprehensive Income [Member]
Reclassification Out of Accumulated Other Comprehensive Income [Line Items]
Fuel and oil	59		101
Less: Tax Expense	22		38
Net of Tax	37		63
Interest rate derivatives | Reclassification out of Accumulated Other Comprehensive Income [Member]
Reclassification Out of Accumulated Other Comprehensive Income [Line Items]
Interest Expense	6		14
Less: Tax Expense	2		5
Net of Tax	$ 4		$ 9