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Financial Derivative Instruments Narrative (Details) - USD ($) $ in Millions | 3 Months Ended | 9 Months Ended
--- | --- | ---
Sep. 30, 2018 | Sep. 30, 2017 | Sep. 30, 2018 | Sep. 30, 2017
Derivative [Line Items] |  |  |  |
Derivative, Cost of Hedge | $ 34 | $ 34 | $ 101 | $ 102
Percentage of actual consumption hedged | 80.00% |  | 80.00% |
Current Unrealized Net Gains (Losses) in OCI | $ 198 |  | $ 198 |
Maximum sum of derivatives of counterparty to be included in other (less than $20 million) | $ 20 |  | $ 20 |
Maximum cash collateral provided as a percentage of derivative contract value (in hundredths) | 100.00% |  | 100.00% |
Maximum letter of credit percent of collateral | 100.00% |  | 100.00% |
Remainder of Current Year |  |  |  |
Derivative [Line Items] |  |  |  |
Derivative, Nonmonetary Notional Amount, Percent of Required Need, Coverage | 79.00% |  | 79.00% |

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- Definition Represents percentage of cash collateral provided on the fair value of fuel derivative contracts when credit rating is non-investment grade. + References No definition available. + Details
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Namespace Prefix: | luv_
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Period Type: | instant

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- Definition Represents the percentage of cash collateral that can be provided with a letter of credit. + References No definition available. + Details
Name: | luv_LetterofCreditPercentofCollateral
Namespace Prefix: | luv_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | instant

X
- Definition Maximum sum of derivatives of a counterparty to be included in Other and no risk of the Company posting collateral. + References No definition available. + Details
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X
- Definition Percentage of actual consumption hedged + References No definition available. + Details
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Period Type: | duration

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- Definition The premium (cost) of a hedge, expensed during the period. + References No definition available. + Details
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Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

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
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- Definition The percentage of expected requirements covered by the aggregate notional amount of derivative contracts expressed in nonmonetary units. For example, the number of barrels specified in a fuel oil forward purchase contract as a percentage of expected need. + References No definition available. + Details
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Namespace Prefix: | us-gaap_
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X
- Definition The estimated net amount of unrealized gains or losses on price risk cash flow hedges as of the balance sheet date expected to be reclassified to earnings within the next twelve months. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 815 -SubTopic 30 -Section 50 -Paragraph 1 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=112277219&loc=d3e80748-113994 + Details
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- Details
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