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Leases (Details) | 3 Months Ended | 12 Months Ended |
--- | --- | --- | ---
Dec. 31, 2018 USD ($) aircraft | Sep. 30, 2017 USD ($) | Dec. 31, 2018 USD ($) aircraft | Dec. 31, 2017 USD ($) aircraft CapitalLeases | Dec. 31, 2016 USD ($) | Jul. 09, 2012 aircraft
Capital Leases, Balance Sheet, Assets by Major Class, Net [Abstract] |  |  |  |  |  |  |
Flight equipment |  | $ 1,329,000,000 |  | $ 1,329,000,000 | $ 1,207,000,000 |  |
Less: accumulated amortization |  | 304,000,000 |  | 304,000,000 | 172,000,000 |  |
Total |  | 1,025,000,000 |  | 1,025,000,000 | $ 1,035,000,000 |  |
Capital Leased Assets [Line Items] |  |  |  |  |  |  |
2019 |  | 111,000,000 |  | 111,000,000 |  |  |
2020 |  | 109,000,000 |  | 109,000,000 |  |  |
2021 |  | 105,000,000 |  | 105,000,000 |  |  |
2022 |  | 100,000,000 |  | 100,000,000 |  |  |
2023 |  | 97,000,000 |  | 97,000,000 |  |  |
Thereafter |  | 335,000,000 |  | 335,000,000 |  |  |
Total minimum lease payments |  | 857,000,000 |  | 857,000,000 |  |  |
Less amount representing interest |  | 126,000,000 |  | 126,000,000 |  |  |
Present value of minimum lease payments (a) | [1] | 731,000,000 |  | 731,000,000 |  |  |
Less current portion |  | 85,000,000 |  | 85,000,000 |  |  |
Long-term portion |  | $ 646,000,000 |  | $ 646,000,000 |  |  |
Number of capital leased assets |  | 72 |  | 72 | 69 |  |
Rental expense for operating leases |  |  |  | $ 935,000,000 | $ 939,000,000 | $ 932,000,000 |
Total Classic aircraft retired in 2017 | aircraft |  |  |  |  | 87 |  |
Remaining -300 aircraft grounded in September 2017 | aircraft |  |  |  |  | 61 |  |
Subleases |  |  |  |  |  |  |
2018 |  | $ (92,000,000) |  | (92,000,000) |  |  |
2019 |  | (78,000,000) |  | (78,000,000) |  |  |
2020 |  | (41,000,000) |  | (41,000,000) |  |  |
2021 |  | (17,000,000) |  | (17,000,000) |  |  |
2022 |  | (7,000,000) |  | (7,000,000) |  |  |
Thereafter |  | (1,000,000) |  | (1,000,000) |  |  |
Total minimum lease payments |  | (236,000,000) |  | (236,000,000) |  |  |
Operating Leased Assets [Line Items] |  |  |  |  |  |  |
Lease Incentive Obligation Excluded |  | $ 114,000,000 |  | $ 114,000,000 |  |  |
Number of operating leased assets | aircraft |  | 51 |  | 51 | 53 |  |
Operating leases |  |  |  |  |  |  |
2019 |  | $ 256,000,000 |  | $ 256,000,000 |  |  |
2020 |  | 279,000,000 |  | 279,000,000 |  |  |
2021 |  | 203,000,000 |  | 203,000,000 |  |  |
2022 |  | 155,000,000 |  | 155,000,000 |  |  |
2023 |  | 139,000,000 |  | 139,000,000 |  |  |
Thereafter |  | 473,000,000 |  | 473,000,000 |  |  |
Total minimum lease payments |  | 1,505,000,000 |  | 1,505,000,000 |  |  |
2019 |  | 348,000,000 |  | 348,000,000 |  |  |
2020 |  | 357,000,000 |  | 357,000,000 |  |  |
2021 |  | 244,000,000 |  | 244,000,000 |  |  |
2022 |  | 172,000,000 |  | 172,000,000 |  |  |
2023 |  | 146,000,000 |  | 146,000,000 |  |  |
Thereafter |  | 474,000,000 |  | 474,000,000 |  |  |
Total minimum lease payments |  | $ 1,741,000,000 |  | 1,741,000,000 |  |  |
Aircraft grounding charge |  |  | $ 63,000,000 | $ 0 | $ 63,000,000 | $ 0 |
Minimum |  |  |  |  |  |  |
Capital Leased Assets [Line Items] |  |  |  |  |  |  |
Renewal term |  | 1 year |  | 1 year |  |  |
Maximum |  |  |  |  |  |  |
Capital Leased Assets [Line Items] |  |  |  |  |  |  |
Renewal term |  | 5 years |  | 5 years |  |  |
Property Subject to Operating Lease [Member] |  |  |  |  |  |  |
Operating Leased Assets [Line Items] |  |  |  |  |  |  |
Number of operating leased assets | aircraft |  | 51 |  | 51 |  |  |
Property Available for Operating Lease [Member] |  |  |  |  |  |  |
Operating Leased Assets [Line Items] |  |  |  |  |  |  |
Number of operating leased assets | aircraft |  | 124 |  | 124 |  |  |
B-717-200 |  |  |  |  |  |  |
Capital Leased Assets [Line Items] |  |  |  |  |  |  |
Number of capital leased assets | aircraft |  | 2 |  | 2 |  |  |
Number of owned assets | aircraft |  | 10 |  | 10 |  |  |
Lease terms for owned aircraft |  | 4 years |  |  |  |  |
Contingent rental payment due |  | $ 0 |  | $ 0 |  |  |
Residual value of leased properties |  | $ 0 |  | $ 0 |  |  |
Operating Leased Assets [Line Items] |  |  |  |  |  |  |
Property Subject To Or Available For Lease, Number Of Units, Total | aircraft |  |  |  |  |  |  | 88
Number of operating leased assets | aircraft |  | 73 |  | 73 |  |  |
B-717-200 | Minimum |  |  |  |  |  |  |
Capital Leased Assets [Line Items] |  |  |  |  |  |  |
Sublease terms |  | 1 year |  |  |  |  |
B-717-200 | Maximum |  |  |  |  |  |  |
Capital Leased Assets [Line Items] |  |  |  |  |  |  |
Sublease terms |  | 6 years |  |  |  |  |
Expired | B-717-200 |  |  |  |  |  |  |
Operating Leased Assets [Line Items] |  |  |  |  |  |  |
Property Subject To Or Available For Lease, Number Of Units, Total | aircraft |  |  |  |  |  |  | 3
[1] | Excludes lease incentive obligation of $114 million.

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