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Financial Derivative Instruments - Collateral by Balance Sheet Location (Details) - Fuel derivatives - USD ($) $ in Millions | Dec. 31, 2018 | Dec. 31, 2017
--- | --- | ---
Derivative [Line Items] |  |
Collateral Already Posted, Aggregate Fair Value | $ 0 |
Prepaid expenses and other current assets |  |
Derivative [Line Items] |  |
Total Collateral Already Received Aggregate Fair Value | 0 | $ 15
Accounts Payable |  |
Derivative [Line Items] |  |
Due To Third Parties For Settled Fuel Contracts | 0 | $ 29
Accounts And Other Receivables [Member] |  |
Derivative [Line Items] |  |
Receivable from third parties for settled fuel contracts - current | $ 2 |

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- Definition Amount due to third parties for settled fuel contracts as of the end of the period reported, recorded in Accrued liabilities on the balance sheet. + References No definition available. + Details
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Namespace Prefix: | luv_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

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- Definition Amount receivable from third parties for settled fuel contracts as of the end of the period reported, recorded in Accounts and other receivables on the balance sheet. + References No definition available. + Details
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Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

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- Definition Total cash, current and noncurrent, that is already received, at the end of the reporting period, as collateral for derivative instruments. + References No definition available. + Details
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Namespace Prefix: | luv_
Data Type: | xbrli:monetaryItemType
Balance Type: | na
Period Type: | instant

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- Definition The aggregate fair value of assets that are already posted, at the end of the reporting period, as collateral for derivative instruments with credit-risk-related contingent features. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 815 -SubTopic 10 -Section 50 -Paragraph 4H -Subparagraph (d) -URI http://asc.fasb.org/extlink&oid=109980867&loc=SL5624258-113959 + Details
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Period Type: | instant

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- Definition Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table. + References No definition available. + Details
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- Details
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Balance Type: |
Period Type: |

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- Details
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- Details
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- Details
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