Fair Value Measurements (Details) (USD $) In Millions, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash Equivalents, at Fair Value	$ 2,126	$ 2,176
Restricted Cash Equivalents and Investments, at Fair Value	290	344
Fuel Contracts, at Fair Value	257	249
Interest Rate Contracts, at Fair Value	(66)	(66)
Foreign Currency Exchange Contracts, at Fair Value	210	123
Short-Term Investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, at Fair Value	958	958
Long-Term Investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, at Fair Value	202	208
Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash Equivalents, at Fair Value	2,126	2,176
Restricted Cash Equivalents and Investments, at Fair Value	290	344
Fuel Contracts, at Fair Value	61	27
Interest Rate Contracts, at Fair Value	0	0
Foreign Currency Exchange Contracts, at Fair Value	0	0
Level 1 | Short-Term Investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, at Fair Value	958	958
Level 1 | Long-Term Investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, at Fair Value	94	100
Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash Equivalents, at Fair Value	0	0
Restricted Cash Equivalents and Investments, at Fair Value	0	0
Fuel Contracts, at Fair Value	196	222
Interest Rate Contracts, at Fair Value	(66)	(66)
Foreign Currency Exchange Contracts, at Fair Value	210	123
Level 2 | Short-Term Investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, at Fair Value	0	0
Level 2 | Long-Term Investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, at Fair Value	27	27
Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash Equivalents, at Fair Value	0	0
Restricted Cash Equivalents and Investments, at Fair Value	0	0
Fuel Contracts, at Fair Value	0	0
Interest Rate Contracts, at Fair Value	0	0
Foreign Currency Exchange Contracts, at Fair Value	0	0
Level 3 | Short-Term Investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, at Fair Value	0	0
Level 3 | Long-Term Investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, at Fair Value	$ 81	$ 81