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Leases (Details) | 3 Months Ended | 12 Months Ended |
--- | --- | --- | ---
Dec. 31, 2017 USD ($) aircraft | Sep. 30, 2017 USD ($) | Dec. 31, 2017 USD ($) aircraft | Dec. 31, 2016 USD ($) aircraft CapitalLeases | Dec. 31, 2015 USD ($) | Jul. 09, 2012 aircraft
Capital Leases, Balance Sheet, Assets by Major Class, Net [Abstract] |  |  |  |  |  |  |
Flight equipment |  | $ 1,207,000,000 |  | $ 1,207,000,000 | $ 923,000,000 |  |
Less: accumulated amortization |  | 172,000,000 |  | 172,000,000 | 82,000,000 |  |
Total |  | 1,035,000,000 |  | 1,035,000,000 | $ 841,000,000 |  |
Capital Leased Assets [Line Items] |  |  |  |  |  |  |
2018 |  | 107,000,000 |  | 107,000,000 |  |  |
2019 |  | 106,000,000 |  | 106,000,000 |  |  |
2020 |  | 105,000,000 |  | 105,000,000 |  |  |
2021 |  | 100,000,000 |  | 100,000,000 |  |  |
2022 |  | 96,000,000 |  | 96,000,000 |  |  |
Thereafter |  | 416,000,000 |  | 416,000,000 |  |  |
Total minimum lease payments |  | 930,000,000 |  | 930,000,000 |  |  |
Less amount representing interest |  | 150,000,000 |  | 150,000,000 |  |  |
Present value of minimum lease payments (a) | [1] | 780,000,000 |  | 780,000,000 |  |  |
Less current portion |  | 79,000,000 |  | 79,000,000 |  |  |
Long-term portion |  | $ 701,000,000 |  | $ 701,000,000 |  |  |
Number of capital leased assets |  | 69 |  | 69 | 51 |  |
Rental expense for operating leases |  |  |  | $ 939,000,000 | $ 932,000,000 | $ 909,000,000 |
Total Classic aircraft retired in 2017 | aircraft |  |  |  | 87 |  |  |
Remaining -300 aircraft grounded in September 2017 | aircraft |  |  |  | 61 |  |  |
Subleases |  |  |  |  |  |  |
2018 |  | $ (102,000,000) |  | $ (102,000,000) |  |  |
2019 |  | (98,000,000) |  | (98,000,000) |  |  |
2020 |  | (78,000,000) |  | (78,000,000) |  |  |
2021 |  | (41,000,000) |  | (41,000,000) |  |  |
2022 |  | (17,000,000) |  | (17,000,000) |  |  |
Thereafter |  | (8,000,000) |  | (8,000,000) |  |  |
Total minimum lease payments |  | (344,000,000) |  | (344,000,000) |  |  |
Operating Leased Assets [Line Items] |  |  |  |  |  |  |
Lease Incentive Obligation Excluded |  | 105,000,000 |  | 105,000,000 |  |  |
Number of operating leased assets | aircraft |  |  |  |  | 83 |  |
Operating leases (b) |  |  |  |  |  |  |
2018 |  | 257,000,000 |  | 257,000,000 |  |  |
2019 |  | 233,000,000 |  | 233,000,000 |  |  |
2020 |  | 186,000,000 |  | 186,000,000 |  |  |
2021 |  | 114,000,000 |  | 114,000,000 |  |  |
2022 |  | 68,000,000 |  | 68,000,000 |  |  |
Thereafter |  | 169,000,000 |  | 169,000,000 |  |  |
Total minimum lease payments |  | 1,027,000,000 |  | 1,027,000,000 |  |  |
2018 | [2] | 359,000,000 |  | 359,000,000 |  |  |
2019 | [2] | 331,000,000 |  | 331,000,000 |  |  |
2020 | [2] | 264,000,000 |  | 264,000,000 |  |  |
2021 | [2] | 155,000,000 |  | 155,000,000 |  |  |
2022 | [2] | 85,000,000 |  | 85,000,000 |  |  |
Thereafter | [2] | 177,000,000 |  | 177,000,000 |  |  |
Total minimum lease payments | [2] | $ 1,371,000,000 |  | 1,371,000,000 |  |  |
Aircraft grounding charge |  |  | $ 63,000,000 | $ 63,000,000 | $ 0 | $ 0 |
Minimum |  |  |  |  |  |  |
Capital Leased Assets [Line Items] |  |  |  |  |  |  |
Renewal term |  |  |  | 1 year |  |  |
Maximum |  |  |  |  |  |  |
Capital Leased Assets [Line Items] |  |  |  |  |  |  |
Renewal term |  |  |  | 5 years |  |  |
B737-300 |  |  |  |  |  |  |
Operating Leased Assets [Line Items] |  |  |  |  |  |  |
Number of operating leased assets | aircraft |  | 15 |  | 15 |  |  |
B-717-200 |  |  |  |  |  |  |
Capital Leased Assets [Line Items] |  |  |  |  |  |  |
Number of capital leased assets | aircraft |  | 2 |  | 2 |  |  |
Number of aircrafts subleased | aircraft |  |  |  |  |  |  | 88
Number of owned assets | aircraft |  | 10 |  | 10 |  |  |
Lease terms for owned aircraft |  | 6 years |  |  |  |  |
Contingent rental payment due |  | $ 0 |  | $ 0 |  |  |
Residual value of leased properties |  | $ 0 |  | $ 0 |  |  |
Operating Leased Assets [Line Items] |  |  |  |  |  |  |
Number of operating leased assets | aircraft |  | 76 |  | 76 |  |  |
B-717-200 | Minimum |  |  |  |  |  |  |
Capital Leased Assets [Line Items] |  |  |  |  |  |  |
Sublease terms |  | 2 years |  |  |  |  |
B-717-200 | Maximum |  |  |  |  |  |  |
Capital Leased Assets [Line Items] |  |  |  |  |  |  |
Sublease terms |  | 7 years |  |  |  |  |
Property Subject to Operating Lease [Member] |  |  |  |  |  |  |
Operating Leased Assets [Line Items] |  |  |  |  |  |  |
Number of operating leased assets | aircraft |  | 53 |  | 53 |  |  |
Property Available for Operating Lease [Member] |  |  |  |  |  |  |
Operating Leased Assets [Line Items] |  |  |  |  |  |  |
Number of operating leased assets | aircraft |  | 144 |  | 144 |  |  |
[1] | Excludes lease incentive obligation of $105 million.
[2] | Includes 15 remaining Classic aircraft on operating leases, which net remaining lease payments were included in the $63 million grounding charge recorded during 2017.

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