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Fair Value Instruments - Carrying and Estimated Fair Value of Debt (Details) $ in Millions | Mar. 31, 2019 USD ($)
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2.75% Notes Due 2019 | Unsecured Debt |
Debt Instrument [Line Items] |
Carrying amount of debt | $ 300
Stated interest rate | 2.75%
Term Loan Agreement payable through May 2019 - 6.315% | Notes Payable to Banks |
Debt Instrument [Line Items] |
Carrying amount of debt | $ 11
Stated interest rate | 6.315%
Term Loan Agreement payable through July 2019 - 4.84% | Notes Payable to Banks |
Debt Instrument [Line Items] |
Carrying amount of debt | $ 5
Stated interest rate | 4.84%
2.65% Notes due 2020 | Unsecured Debt |
Debt Instrument [Line Items] |
Carrying amount of debt | $ 495
Stated interest rate | 2.65%
Term Loan Agreement payable through 2020 - 5.223% | Notes Payable to Banks |
Debt Instrument [Line Items] |
Carrying amount of debt | $ 174
Stated interest rate | 5.223%
737 Aircraft Notes payable through 2020 | Notes Payable to Banks |
Debt Instrument [Line Items] |
Carrying amount of debt | $ 45
2.75% Notes due 2022 | Unsecured Debt |
Debt Instrument [Line Items] |
Carrying amount of debt | $ 300
Stated interest rate | 2.75%
Pass Through Certificates due 2022 - 6.24% | Enhanced Equipment Trust Certificate |
Debt Instrument [Line Items] |
Carrying amount of debt | $ 225
Stated interest rate | 6.24%
Term Loan Agreement due 2026 - 3.62% | Notes Payable to Banks |
Debt Instrument [Line Items] |
Carrying amount of debt | $ 197
Stated interest rate | 3.88%
3.00% Notes due 2026 | Unsecured Debt |
Debt Instrument [Line Items] |
Carrying amount of debt | $ 300
Stated interest rate | 3.00%
3.45% Notes due 2027 | Unsecured Debt |
Debt Instrument [Line Items] |
Carrying amount of debt | $ 300
Stated interest rate | 3.45%
7.375% Debentures due 2027 | Unsecured Debt |
Debt Instrument [Line Items] |
Carrying amount of debt | $ 124
Stated interest rate | 7.375%
Level 2 | 2.75% Notes Due 2019 | Unsecured Debt |
Debt Instrument [Line Items] |
Notes Payable, Fair Value | $ 300
Level 2 | 2.65% Notes due 2020 | Unsecured Debt |
Debt Instrument [Line Items] |
Notes Payable, Fair Value | 494
Level 2 | 2.75% Notes due 2022 | Unsecured Debt |
Debt Instrument [Line Items] |
Notes Payable, Fair Value | 299
Level 2 | Pass Through Certificates due 2022 - 6.24% | Enhanced Equipment Trust Certificate |
Debt Instrument [Line Items] |
Notes Payable, Fair Value | 236
Level 2 | 3.00% Notes due 2026 | Unsecured Debt |
Debt Instrument [Line Items] |
Notes Payable, Fair Value | 290
Level 2 | 3.45% Notes due 2027 | Unsecured Debt |
Debt Instrument [Line Items] |
Notes Payable, Fair Value | 298
Level 2 | 7.375% Debentures due 2027 | Unsecured Debt |
Debt Instrument [Line Items] |
Loans Payable, Fair Value | 148
Level 3 | Term Loan Agreement payable through May 2019 - 6.315% | Notes Payable to Banks |
Debt Instrument [Line Items] |
Loans Payable, Fair Value | 11
Level 3 | Term Loan Agreement payable through July 2019 - 4.84% | Notes Payable to Banks |
Debt Instrument [Line Items] |
Loans Payable, Fair Value | 5
Level 3 | Term Loan Agreement payable through 2020 - 5.223% | Notes Payable to Banks |
Debt Instrument [Line Items] |
Loans Payable, Fair Value | 174
Level 3 | 737 Aircraft Notes payable through 2020 | Notes Payable to Banks |
Debt Instrument [Line Items] |
Notes Payable, Fair Value | 44
Level 3 | Term Loan Agreement due 2026 - 3.62% | Notes Payable to Banks |
Debt Instrument [Line Items] |
Loans Payable, Fair Value | $ 197

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- Definition Amount, before unamortized (discount) premium and debt issuance costs, of long-term debt. Includes, but is not limited to, notes payable, bonds payable, commercial loans, mortgage loans, convertible debt, subordinated debt and other types of debt. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 470 -SubTopic 20 -Section 50 -Paragraph 4 -Subparagraph (b)(1) -URI http://asc.fasb.org/extlink&oid=109500613&loc=SL6031897-161870 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 210 -Section S99 -Paragraph 1 -Subparagraph (SX 210.7-03(16)) -URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910 Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02(22)) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 Reference 4: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 210 -Section S99 -Paragraph 1 -Subparagraph (SX 210.9-03(16)) -URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878 + Details
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