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Significant Accounting Policies - Narrative (Details) - USD ($) $ in Millions | 3 Months Ended | 12 Months Ended |  |
--- | --- | --- | --- | ---
Dec. 31, 2018 | Sep. 30, 2018 | Jun. 30, 2018 | Mar. 31, 2018 | Dec. 31, 2017 | Sep. 30, 2017 | Jun. 30, 2017 | Mar. 31, 2017 | Dec. 31, 2018 | Dec. 31, 2017 | Dec. 31, 2016 | Jan. 01, 2018 | Jan. 01, 2017
Summary Of Significant Accounting Policies [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Revenue | $ 10,491 | $ 11,003 | $ 10,777 | $ 9,032 | $ 9,451 | $ 9,899 | $ 10,008 | $ 8,426 | $ 41,303 | $ 37,784 | [1] | $ 36,558 | [1] |  |
Period of member account inactivity at which miles expire |  |  |  |  |  |  |  |  | 18 months |  |  |  |  |  |
Carrying value of computer software | $ 359 |  |  |  | $ 345 |  |  |  | $ 359 | 345 |  |  |  |  |
Residual value | 10.00% |  |  |  |  |  |  |  | 10.00% |  |  |  |  |  |
Advertising expense |  |  |  |  |  |  |  |  | $ 211 | 217 |  | 220 |  |  |
Reclassification to retained earnings upon adoption of accounting standard |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ (14)
Retained Earnings (Accumulated Deficit) |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Summary Of Significant Accounting Policies [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Reclassification to retained earnings upon adoption of accounting standard |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 6 | $ (14)
ASU 2016-01 | Retained Earnings (Accumulated Deficit) |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Summary Of Significant Accounting Policies [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Reclassification to retained earnings upon adoption of accounting standard |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 6 |
Minimum |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Summary Of Significant Accounting Policies [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Frequent flier program expiration period |  |  |  |  |  |  |  |  | 1 year |  |  |  |  |  |
Maximum |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Summary Of Significant Accounting Policies [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Frequent flier program expiration period |  |  |  |  |  |  |  |  | 8 years |  |  |  |  |  |
Aircraft Seats | Minimum |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Summary Of Significant Accounting Policies [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Estimated useful life |  |  |  |  |  |  |  |  | 10 years |  |  |  |  |  |
Aircraft Seats | Maximum |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Summary Of Significant Accounting Policies [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Estimated useful life |  |  |  |  |  |  |  |  | 15 years |  |  |  |  |  |
Aircraft and Aircraft Spare Parts |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Summary Of Significant Accounting Policies [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Residual value | 10.00% |  |  |  |  |  |  |  | 10.00% |  |  |  |  |  |
Computer Software |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Summary Of Significant Accounting Policies [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Depreciation expense |  |  |  |  |  |  |  |  | $ 122 | 117 |  | 108 |  |  |
Computer Software | Minimum |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Summary Of Significant Accounting Policies [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Estimated useful life |  |  |  |  |  |  |  |  | 5 years |  |  |  |  |  |
Computer Software | Maximum |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Summary Of Significant Accounting Policies [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Estimated useful life |  |  |  |  |  |  |  |  | 15 years |  |  |  |  |  |
Passenger Revenue |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Summary Of Significant Accounting Policies [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Ancillary fees |  |  |  |  |  |  |  |  | $ 2,200 | 2,000 |  | 1,900 |  |  |
Passenger Revenue |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Summary Of Significant Accounting Policies [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Revenue |  |  |  |  |  |  |  |  | 37,706 | 34,460 | [1] | 33,429 | [1] |  |
Other Operating Revenue |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Summary Of Significant Accounting Policies [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Revenue |  |  |  |  |  |  |  |  | 2,360 | 2,210 | [1] | 2,195 | [1] |  |
Other Operating Revenue | Chase and Other Partner Agreements |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Summary Of Significant Accounting Policies [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Revenue |  |  |  |  |  |  |  |  | 2,000 | 1,800 |  | $ 1,700 |  |  |
Transportation Advance Ticket Arrangement | Passenger Revenue |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Summary Of Significant Accounting Policies [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Revenue |  |  |  |  |  |  |  |  | $ 3,100 | $ 2,900 |  |  |  |  |
[1] | Amounts adjusted due to the adoption of Accounting Standards Update No. 2014-09, Revenue from Contracts with Customers (Topic 606) and Accounting Standards Update No. 2017-07, Improving the Presentation of Net Periodic Pension Cost and Net Periodic Postretirement Benefit Cost. See Note 1 to the financial statements contained in Part II, Item 8 of this report for additional information.

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