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Schedule of Effect of Four Quarters Events (Detail) - USD ($) $ in Millions | 3 Months Ended | 12 Months Ended
--- | --- | ---
Dec. 31, 2017 | Sep. 30, 2017 | Jun. 30, 2017 | Mar. 31, 2017 | Dec. 31, 2016 | Sep. 30, 2016 | Jun. 30, 2016 | Mar. 31, 2016 | Dec. 31, 2017 | Dec. 31, 2016 | Dec. 31, 2015
Operating: |  |  |  |  |  |  |  |  |  |  |
Severance and benefit costs | $ 15 | $ 23 | $ 41 | $ 37 | $ 10 | $ 13 | $ 6 | $ 8 | $ 116 | $ 37 | $ 107
Impairment of assets | 10 | 15 |  |  |  |  | 412 |  | 25 | 412 | 79
(Gains) losses on sale of assets and other special charges | 6 | 12 | 3 | 14 | 19 | 18 | 6 | 8 | 35 | 51 | 122
Total operating special charges | 31 | 50 | 44 | 51 | (31) | 45 | 434 | 190 | 176 | 638 | 326
Labor agreement costs and related items |  |  |  |  | (60) | 14 | 10 | 100 |  | 64 | 18
Income taxes: |  |  |  |  |  |  |  |  |  |  |
Income tax benefit related to special charges | (11) | (18) | (16) | (18) | 12 | (16) | (153) | (72) | (63) | (229) | (11)
Income tax adjustments (Note 7) | (192) |  |  |  | 180 |  |  |  | (192) | 180 | (3,130)
Total operating and nonoperating special charges, net of income taxes and income tax adjustments | (172) | 32 | 28 | 33 | 161 | 29 | 272 | 126 | (79) | 588 | (2,613)
Cleveland airport lease restructuring |  |  |  |  |  |  |  | 74 |  | 74 |
Severance and benefit costs | 15 | 23 | 41 | 37 | 10 | 13 | 6 | 8 | 116 | 37 | 107
Impairment of assets | 10 | 15 |  |  |  |  | 412 |  | 25 | 412 | 79
(Gains) losses on sale of assets and other special charges | 6 | 12 | 3 | 14 | 19 | 18 | 6 | 8 | 35 | 51 | 122
Total operating special charges | 31 | 50 | 44 | 51 | (31) | 45 | 434 | 190 | 176 | 638 | 326
Nonoperating income (expense): |  |  |  |  |  |  |  |  |  |  |
Losses (gain) on extinguishment of debt and other |  |  |  |  |  |  | (9) | 8 |  | (1) | 202
Income tax expense (benefit) related to special charges | (11) | (18) | (16) | (18) | 12 | (16) | (153) | (72) | (63) | (229) | (11)
Income tax adjustments (Note 6) | (192) |  |  |  | 180 |  |  |  | (192) | 180 | (3,130)
Total operating and nonoperating special charges, net of income taxes and income tax adjustments | $ (172) | $ 32 | $ 28 | $ 33 | $ 161 | $ 29 | $ 272 | $ 126 | $ (79) | $ 588 | $ (2,613)

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