Financial Derivative Instruments - Offsetting of Derivative Assets (Details) (USD $) In Millions, unless otherwise specified	Mar. 31, 2014		Dec. 31, 2013
Offsetting Assets [Line Items]
Asset derivative contracts, net	$ 183		$ 145
Fuel derivatives | Prepaid expenses and other current assets
Offsetting Assets [Line Items]
Gross amounts of recognized assets	212		249
Gross liability amounts offset in the Balance Sheet	(169)		(182)
Asset derivative contracts, net	43		67
Fuel derivatives | Other Assets
Offsetting Assets [Line Items]
Gross amounts of recognized assets	234		225
Gross liability amounts offset in the Balance Sheet	(69)		(100)
Asset derivative contracts, net	165	[1]	125	[1]
Fuel derivatives | Accrued Liabilities
Offsetting Assets [Line Items]
Gross amounts of recognized assets	0		9
Gross liability amounts offset in the Balance Sheet	0		(9)
Asset derivative contracts, net	0	[1]	0	[1]
Interest rate derivatives | Other Assets
Offsetting Assets [Line Items]
Gross amounts of recognized assets	18		20
Gross liability amounts offset in the Balance Sheet	0		0
Asset derivative contracts, net	$ 18	[1]	$ 20	[1]

[1] The net amounts of derivative assets and liabilities are reconciled to the individual line item amounts presented in the unaudited Condensed Consolidated Balance Sheet in Note 5.