Comprehensive Income - Reclassification out of Accumulated Other Comprehensive Income (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013
Reclassification Out of Accumulated Other Comprehensive Income [Line Items]
Fuel and oil	$ (1,314)	$ (1,457)
Less: Tax Expense	92	35
Interest rate derivatives | Reclassification out of Accumulated Other Comprehensive Income [Member]
Reclassification Out of Accumulated Other Comprehensive Income [Line Items]
Interest Expense	6
Less: Tax Expense	2
Net of Tax	$ 4