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Financial Derivative Instruments - Collateral by Balance Sheet Location (Details) - Fuel derivatives - USD ($) $ in Millions | Sep. 30, 2019 | Dec. 31, 2018
--- | --- | ---
Accounts Payable |  |
Derivative [Line Items] |  |
Due to third parties for fuel contracts | $ 1 | $ 0
Accounts And Other Receivables |  |
Derivative [Line Items] |  |
Receivable from third parties for settled fuel contracts - current | $ 0 | $ 2

X
- 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
Name: | luv_DueToThirdPartiesForSettledFuelContracts
Namespace Prefix: | luv_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- 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
Name: | luv_ReceivableFromThirdPartiesForSettledFuelContractsCurrent
Namespace Prefix: | luv_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- 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
Name: | us-gaap_DerivativeLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

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- Details
Name: | us-gaap_BalanceSheetLocationAxis=luv_AccountsPayableBalanceSheetLocationMemberDomain
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

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- Details
Name: | us-gaap_DerivativeInstrumentRiskAxis=us-gaap_CommodityContractMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_BalanceSheetLocationAxis=luv_AccountsAndOtherReceivablesMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |