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GENERAL AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Tables) | 12 Months Ended
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Dec. 31, 2017
Accounting Policies [Abstract] |
Property, Plant and Equipment [Table Text Block] | Property and equipment are recorded at cost and depreciated using the straight-line method over their estimated useful lives less an estimated salvage value, which are as follows:
| Estimated Useful Life | Estimated Salvage Value
Aircraft and other flight equipment: |  |
Boeing 737, Airbus A319/320, and E175 aircraft | 20-25 years | 10%
Bombardier Q400 aircraft | 15 years | 10%
Buildings | 25 - 30 years | —%
Minor building and land improvements | 10 years | —%
Capitalized leases and leasehold improvements | Generally shorter of lease term or estimated useful life | 0-10%
Computer hardware and software | 3-10 years | —%
Other furniture and equipment | 5-10 years | —%
Liabilities from Mileage Plan [Table Text Block] | Frequent flyer program deferred revenue and liabilities included in the consolidated balance sheets (in millions):
| 2017 |  | 2016
Current Liabilities: |  |  |
Other accrued liabilities | $ | 519 |  |  | $ | 484 |
Other Liabilities and Credits: |  |  |  |  |
Deferred revenue | 699 |  |  | 638 |
Other liabilities | 26 |  |  | 21 |
Total | $ | 1,244 |  |  | $ | 1,143 |
Revenue from Mileage Plan [Table Text Block] | Frequent flyer program revenue included in the consolidated statements of operations (in millions):
| 2017 |  | 2016 |  | 2015
Passenger revenues | $ | 380 |  |  | $ | 293 |  |  | $ | 267 |
Other—net revenues | 482 |  |  | 429 |  |  | 329 |
Total frequent flyer program revenues | $ | 862 |  |  | $ | 722 |  |  | $ | 596 |

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- Definition Tabular disclosure of physical assets used in the normal conduct of business and not intended for resale. Includes, but is not limited to, balances by class of assets, depreciation and depletion expense and method used, including composite depreciation, and accumulated deprecation. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 360 -SubTopic 10 -Section 50 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=6391035&loc=d3e2868-110229 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02(13)) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 + Details
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