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Pension and Other Postretirement Plans (Defined Pension and Other Postretirement Plans) - Additional Information (Detail) - USD ($) $ in Millions | 12 Months Ended
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Dec. 31, 2018 | Dec. 31, 2017 | Dec. 31, 2016
Defined Benefit Plan Disclosure [Line Items] |  |  |
Effect on post retirement benefit obligation, 1% Decrease |  | $ 185 |
Effect on benefit expense, 1% Decrease |  | 8 |
Other Postretirement Benefits |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Employer contributions |  | $ 108 | $ 119
Other Postretirement Benefits | Deposit Administration Fund |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Target allocation of plan assets |  | 100.00% |
Pension Benefits |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Employer contributions |  | $ 419 | $ 421
United Airlines, Inc. | Other Postretirement Benefits | Scenario Forecast |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Employer contributions | $ 109 |  |
United Airlines, Inc. | Pension Benefits | Scenario Forecast |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Employer contributions | $ 420 |  |

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- Definition Defined Benefit Plan Effect Of One Percentage Point Decrease In Discount Rate On Net Benefit Cost + References No definition available. + Details
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- Definition Amount of contribution received by defined benefit plan from employer which increases plan assets. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (d)(5)(ii) -URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e1928-114920 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 6 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e2709-114920 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (b)(3) -URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e1928-114920 Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (d)(5)(iv)(01) -URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e1928-114920 + Details
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- Definition Percentage of target investment allocation to total plan assets. Includes, but is not limited to, percentage on weighted-average basis if more than one plan. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (d)(5)(i) -URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e1928-114920 + Details
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