Fair Value Instruments - Carrying and Estimated Fair Value of Debt (Details) (USD $) In Millions, unless otherwise specified	Jun. 30, 2013
5.25% Notes due 2014 | Unsecured Debt
Debt Instrument [Line Items]
Carrying amount of debt	$ 362
Stated interest rate	5.25%
5.75% Notes due 2016 | Unsecured Debt
Debt Instrument [Line Items]
Carrying amount of debt	322
Stated interest rate	5.75%
5.25% Convertible Senior Notes due 2016 | Convertible Debt
Debt Instrument [Line Items]
Carrying amount of debt	116
Stated interest rate	5.25%
5.125% Notes due 2017 | Unsecured Debt
Debt Instrument [Line Items]
Carrying amount of debt	326
Stated interest rate	5.125%
Fixed-rate 717 Aircraft Notes payable through 2017 - 10.38% | Enhanced Equipment Trust Certificate
Debt Instrument [Line Items]
Carrying amount of debt	56
Stated interest rate	10.38%
French Credit Agreements due 2018 - 1.12% | Notes Payable to Banks
Debt Instrument [Line Items]
Carrying amount of debt	51
Stated interest rate	1.12%
Fixed-rate 737 Aircraft Notes payable through 2018 - 7.02% | Notes Payable to Banks
Debt Instrument [Line Items]
Carrying amount of debt	33
Stated interest rate	7.02%
Term Loan Agreement due 2019 - 6.315% | Notes Payable to Banks
Debt Instrument [Line Items]
Carrying amount of debt	226
Stated interest rate	6.315%
Term Loan Agreement due 2019 - 6.84% | Notes Payable to Banks
Debt Instrument [Line Items]
Carrying amount of debt	90
Stated interest rate	6.84%
Term Loan Agreement due 2020 - 5.223% | Notes Payable to Banks
Debt Instrument [Line Items]
Carrying amount of debt	432
Stated interest rate	5.223%
Floating-rate 737 Aircraft Notes payable through 2020 | Notes Payable to Banks
Debt Instrument [Line Items]
Carrying amount of debt	359
Pass Through Certificates due 2022 - 6.24% | Enhanced Equipment Trust Certificate
Debt Instrument [Line Items]
Carrying amount of debt	385
Stated interest rate	6.24%
7.375% Debentures due 2027 | Unsecured Debt
Debt Instrument [Line Items]
Carrying amount of debt	137
Stated interest rate	7.375%
Level 2 | 5.25% Notes due 2014 | Unsecured Debt
Debt Instrument [Line Items]
Notes Payable, Fair Value	376
Level 2 | 5.75% Notes due 2016 | Unsecured Debt
Debt Instrument [Line Items]
Notes Payable, Fair Value	355
Level 2 | 5.25% Convertible Senior Notes due 2016 | Convertible Debt
Debt Instrument [Line Items]
Notes Payable, Fair Value	143
Level 2 | 5.125% Notes due 2017 | Unsecured Debt
Debt Instrument [Line Items]
Notes Payable, Fair Value	347
Level 2 | Fixed-rate 717 Aircraft Notes payable through 2017 - 10.38% | Enhanced Equipment Trust Certificate
Debt Instrument [Line Items]
Notes Payable, Fair Value	54
Level 2 | Pass Through Certificates due 2022 - 6.24% | Enhanced Equipment Trust Certificate
Debt Instrument [Line Items]
Notes Payable, Fair Value	440
Level 2 | 7.375% Debentures due 2027 | Unsecured Debt
Debt Instrument [Line Items]
Loans Payable, Fair Value	145
Level 3 | French Credit Agreements due 2018 - 1.12% | Notes Payable to Banks
Debt Instrument [Line Items]
Notes Payable, Fair Value	51
Level 3 | Fixed-rate 737 Aircraft Notes payable through 2018 - 7.02% | Notes Payable to Banks
Debt Instrument [Line Items]
Notes Payable, Fair Value	34
Level 3 | Term Loan Agreement due 2019 - 6.315% | Notes Payable to Banks
Debt Instrument [Line Items]
Loans Payable, Fair Value	228
Level 3 | Term Loan Agreement due 2019 - 6.84% | Notes Payable to Banks
Debt Instrument [Line Items]
Loans Payable, Fair Value	96
Level 3 | Term Loan Agreement due 2020 - 5.223% | Notes Payable to Banks
Debt Instrument [Line Items]
Loans Payable, Fair Value	402
Level 3 | Floating-rate 737 Aircraft Notes payable through 2020 | Notes Payable to Banks
Debt Instrument [Line Items]
Notes Payable, Fair Value	$ 352