Fair Value Measurements (Summary Of Assets And Liabilities Measured At Fair Value On Recurring Basis) (Details) (USD $) In Millions, unless otherwise specified	Sep. 30, 2013		Dec. 31, 2012
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Restricted Cash and Investments, Current	$ 935		$ 850
Fair Value, Equity, Level 1 to Level 2 Transfers, Amount	56
Total [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities, Fair Value Disclosure	6,046
Restricted Cash and Investments, Current	935	[1]
Fuel derivative contracts, fair value, net	58	[1]
Fair value of assets and liabilities measured on recurring basis	7,039
Total [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	545	[1],[2]
Total [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	1,136	[1],[2]
Total [Member] | Repurchase Investments [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities, Fair Value Disclosure	205	[1],[2]
Total [Member] | Corporate Obligations [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities, Fair Value Disclosure	3,448	[1],[2]
Total [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	712	[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	545
Restricted Cash and Investments, Current	879	[1]
Fuel derivative contracts, fair value, net	0	[1]
Fair value of assets and liabilities measured on recurring basis	1,424
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	545	[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	0	[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	0	[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	5,501
Restricted Cash and Investments, Current	56	[1]
Fuel derivative contracts, fair value, net	58	[1]
Fair value of assets and liabilities measured on recurring basis	5,615
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	1,136	[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	205	[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	3,448	[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	712	[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	[1]
Fuel derivative contracts, fair value, net	0	[1]
Fair value of assets and liabilities measured on recurring basis	0	[2]
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	635
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	1,600
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	$ 450

[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) at each measurement date.

[2] The Company’s short-term investments mature in one year or less except for $450 million of Bank notes, $635 million of U.S. Government obligations and $1.6 billion of Corporate obligations which have maturity dates exceeding one year.