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Summary of Significant Accounting Policies - Changes in Accounting Principles (Details) - USD ($) $ in Millions | 12 Months Ended
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Dec. 31, 2018 | Dec. 31, 2017 | Dec. 31, 2016
Changes in Accounting Principles [Abstract] |  |  |
Aircraft rentals | $ 161 | $ 198 | $ 229

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- Definition Changes in Accounting Principles [Abstract] + References No definition available. + Details
Name: | luv_ChangesinAccountingPrinciplesAbstract
Namespace Prefix: | luv_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

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- Definition Expenses incurred related to the lease of aircraft from outside third parties that are used in the entity's business operations. + References No definition available. + Details
Name: | us-gaap_AircraftRental
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration