Comprehensive Income - Reclassification out of Accumulated Other Comprehensive Income (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
Reclassification Out of Accumulated Other Comprehensive Income [Line Items]
Fuel and oil	$ 1,457	$ 1,510
Less: Tax Expense	35	61
Reclassification out of Accumulated Other Comprehensive Income [Member]
Reclassification Out of Accumulated Other Comprehensive Income [Line Items]
Net of Tax	31
Fuel derivatives | Reclassification out of Accumulated Other Comprehensive Income [Member]
Reclassification Out of Accumulated Other Comprehensive Income [Line Items]
Fuel and oil	(42)
Less: Tax Expense	16
Net of Tax	26
Interest rate derivatives | Reclassification out of Accumulated Other Comprehensive Income [Member]
Reclassification Out of Accumulated Other Comprehensive Income [Line Items]
Interest Expense	8
Less: Tax Expense	3
Net of Tax	$ 5