Fair Value Measurements (Summary Of Assets And Liabilities Measured At Fair Value On Recurring Basis) (Details) (USD $) In Millions, unless otherwise specified	Jun. 30, 2012		Dec. 31, 2011
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities, Fair Value Disclosure	$ 4,609
Restricted Cash and Investments, Current	772		738
Fuel derivative contracts, Fair Value	24		97
Fair value of assets and liabilities measured on recurring basis	5,405
Money Market Funds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities, Fair Value Disclosure	490	[1],[2]
Government Agency Investments [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities, Fair Value Disclosure	613	[1],[2]
Repurchase Investments [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities, Fair Value Disclosure	360	[1],[2]
Corporate Obligations [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities, Fair Value Disclosure	2,309	[1],[2]
Bank Notes/Certificates Of Deposit/Time Deposits [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities, Fair Value Disclosure	837	[1],[2]
Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities, Fair Value Disclosure	490
Restricted Cash and Investments, Current	772	[2]
Fuel derivative contracts, Fair Value	0	[2]
Fair value of assets and liabilities measured on recurring basis	1,262
Level 1 [Member] | Money Market Funds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities, Fair Value Disclosure	490	[1],[2]
Level 1 [Member] | Government Agency Investments [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities, Fair Value Disclosure	0	[1],[2]
Level 1 [Member] | Repurchase Investments [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities, Fair Value Disclosure	0	[1],[2]
Level 1 [Member] | Corporate Obligations [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities, Fair Value Disclosure		[1],[2]
Level 1 [Member] | Bank Notes/Certificates Of Deposit/Time Deposits [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities, Fair Value Disclosure		[1],[2]
Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities, Fair Value Disclosure	4,119
Restricted Cash and Investments, Current	0	[1]
Fuel derivative contracts, Fair Value	24	[2]
Fair value of assets and liabilities measured on recurring basis	4,143
Level 2 [Member] | Money Market Funds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities, Fair Value Disclosure	0	[1],[2]
Level 2 [Member] | Government Agency Investments [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities, Fair Value Disclosure	613	[1],[2]
Level 2 [Member] | Repurchase Investments [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities, Fair Value Disclosure	360	[1],[2]
Level 2 [Member] | Corporate Obligations [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities, Fair Value Disclosure	2,309	[1],[2]
Level 2 [Member] | Bank Notes/Certificates Of Deposit/Time Deposits [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities, Fair Value Disclosure	837	[1],[2]
Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities, Fair Value Disclosure	0
Restricted Cash and Investments, Current	0	[2]
Fuel derivative contracts, Fair Value	0	[2]
Fair value of assets and liabilities measured on recurring basis	0	[1]
Level 3 [Member] | Money Market Funds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities, Fair Value Disclosure	0	[1],[2]
Level 3 [Member] | Government Agency Investments [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities, Fair Value Disclosure	0	[1],[2]
Level 3 [Member] | Repurchase Investments [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities, Fair Value Disclosure	0	[1],[2]
Level 3 [Member] | Corporate Obligations [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities, Fair Value Disclosure	0	[1],[2]
Level 3 [Member] | Bank Notes/Certificates Of Deposit/Time Deposits [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities, Fair Value Disclosure	0	[1],[2]
Maturity Dates Exceeding One Year [Member] | Government Agency Investments [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities, Fair Value Disclosure	613
Maturity Dates Exceeding One Year [Member] | Corporate Obligations [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities, Fair Value Disclosure	524
Maturity Dates Exceeding One Year [Member] | Bank Notes/Certificates Of Deposit/Time Deposits [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities, Fair Value Disclosure	$ 262

[1] 2. The Company’s short-term investments mature in one year or less except for $262 million of Bank notes/Certificates of deposit/Time deposits, $613 million of U.S. Government agency investments and $524 million of Corporate obligations which have maturity dates exceeding one year.

[2] 1. Unrealized gains or losses on short-term investments, restricted cash and short-term investments and derivatives qualifying for hedge accounting are recorded in Accumulated other comprehensive income (loss) (OCI) at each measurement date.