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Supplemental Financial Information - Other Non-Current Liabilities (Details) - USD ($) $ in Millions | 3 Months Ended | 12 Months Ended
--- | --- | ---
Sep. 30, 2017 | Dec. 31, 2017 | Dec. 31, 2016 | Dec. 31, 2015
Other Liabilities, Noncurrent [Abstract] |  |  |  |  |  |
Postretirement obligation |  |  | $ 275 |  | $ 256 |
Non-current lease-related obligations |  |  | 85 |  | 125 |
Permanently grounded aircraft liability noncurrent |  |  | 13 | [1] | 0 |
Other deferred compensation |  |  | 237 |  | 204 |
Other |  |  | 76 |  | 108 |
Other non-current liabilities |  |  | 707 |  | 728 |
Write off of Prepaid Rent On Grounded Aircraft |  |  | 15 |  |  |
Aircraft grounding charge |  | $ 63 | 63 |  | 0 | $ 0
Other Noncurrent Liabilities |  |  |  |  |  |
Other Liabilities, Noncurrent [Abstract] |  |  |  |  |  |
Derivative contracts |  |  | 21 |  | 35 |
Other Noncurrent Liabilities | Interest Rate Swap |  |  |  |  |  |
Other Liabilities, Noncurrent [Abstract] |  |  |  |  |  |
Derivative contracts | [2] |  | $ 21 |  | $ 35 |
[1] | These amounts represent the current and noncurrent portion of the Company's cease-use liability recorded during third quarter 2017, as a result of the Company grounding its remaining leased Boeing 737-300 aircraft on September 29, 2017. The liability reflects the remaining net lease payments due and certain lease return requirements that could have to be performed on these leased aircraft prior to their return to the lessors as of the cease-use date, but does not include the write–off of approximately $15 million in net prepaid rents associated with the aircraft at the grounding date, which were included in the $63 million charge recorded. See Note 7 for further information. This loss related to the grounding of the Classic fleet was recorded to Other operating expenses in the Consolidated Statement of Income during third quarter 2017. Approximately $3 million of this liability was paid during fourth quarter 2017.
[2] | The net amounts of derivative assets and liabilities are reconciled to the individual line item amounts presented in the Consolidated Balance Sheet in Note 5.

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