Basis of Presentation (Policies)	3 Months Ended
Basis of Presentation (Policies)	Mar. 31, 2020
Accounting Policies [Abstract]
Basis of Presentation	The unaudited Condensed Consolidated Financial Statements for the interim periods ended March 31, 2020 and 2019 include all adjustments which are, in the opinion of management, necessary for a fair presentation of the results for the interim periods. This includes all normal and recurring adjustments and elimination of significant intercompany transactions. Financial results for the Company and airlines in general can be seasonal in nature. In many years, the Company's revenues, as well as its Operating income and Net income, have been better in its second and third fiscal quarters than in its first and fourth fiscal quarters. Air travel is also significantly impacted by general economic conditions, the amount of disposable income available to consumers, unemployment levels, corporate travel budgets, extreme or severe weather and natural disasters, fears of terrorism or war, impact of fears or actual outbreak of disease or pandemics, and other factors beyond the Company's control. These and other factors, such as the price of jet fuel in some periods, the nature of the Company's fuel hedging program, and the periodic volatility of commodities used by the Company for hedging jet fuel, have created, and may continue to create, significant volatility in the Company's financial results. See Note 4 for further information on fuel and the Company's hedging program. Operating results for the three months ended March 31, 2020, are not necessarily indicative of the results that may be expected for future quarters or for the year ended December 31, 2020. For further information, refer to the Consolidated Financial Statements and footnotes thereto included in the Company's Annual Report on Form 10-K for the year ended December 31, 2019.
Derivatives	Upon proper qualification, the Company accounts for its fuel derivative instruments as cash flow hedges. All periodic changes in fair value of the derivatives designated as hedges are recorded in Accumulated other comprehensive income (loss) ("AOCI") until the underlying jet fuel is consumed. See Note 5. The Company's results are subject to the possibility that the derivatives will no longer qualify for hedge accounting, in which case any change in the fair value of derivative instruments since the last reporting period would be recorded in Other (gains) losses, net, in the unaudited Condensed Consolidated Statement of Comprehensive Income (Loss) in the period of the change; however, any amounts previously recorded to AOCI would remain there until such time as the original forecasted transaction occurs, at which time these amounts would be reclassified to Fuel and oil expense. Factors that have and may continue to lead to the loss of hedge accounting include: significant fluctuation in energy prices, significant weather events affecting refinery capacity and the production of refined products, and the volatility of the different types of products the Company uses in hedging. Increased volatility in these commodity markets for an extended period of time, especially if such volatility were to worsen, could cause the Company to lose hedge accounting altogether for the commodities used in its fuel hedging program, which would create further volatility in the Company’s GAAP financial results. However, even though derivatives may not qualify for hedge accounting, the Company continues to hold the instruments as management believes derivative instruments continue to afford the Company the opportunity to stabilize jet fuel costs. When the Company has sold derivative positions in order to effectively "close" or offset a derivative already held as part of its fuel derivative instrument portfolio, any subsequent changes in fair value of those positions are marked to market through earnings. Likewise, any changes in fair value of those positions that were offset by entering into the sold positions and were de-designated as hedges are concurrently marked to market through earnings. However, any changes in value related to hedges that were deferred as part of AOCI while designated as a hedge would remain until the originally forecasted transaction occurs. In a situation where it becomes probable that a fuel hedged forecasted transaction will not occur, any gains and/or losses that have been recorded to AOCI would be required to be immediately reclassified into earnings. During first quarter 2020, as a result of the drastic drop in demand for air travel, the Company's forecast for second quarter fuel purchases and consumption was significantly reduced, causing the Company to be in an estimated "over– hedged" position for second quarter 2020. Therefore, the Company de–designated a portion of its fuel hedges related to second quarter 2020 and has reclassified approximately $2 million in losses from AOCI into Other (gains) losses, net, in first quarter 2020. The Company did not have any such situations occur during 2019. The Company is party to certain interest rate swap agreements that are accounted for as either fair value hedges or cash flow hedges, as defined in the applicable accounting guidance for derivative instruments and hedging. Several of the Company's interest rate swap agreements qualify for the "shortcut" method of accounting for hedges, which dictates that the hedges are assumed to be perfectly effective, and thus there is no ineffectiveness to be recorded in earnings.
Fair Value of Financial Instruments	Accounting standards pertaining to fair value measurements establish a three-tier fair value hierarchy, which prioritizes the inputs used in measuring fair value. These tiers include: Level 1, defined as observable inputs such as quoted prices in active markets; Level 2, defined as inputs other than quoted prices in active markets that are either directly or indirectly observable; and Level 3, defined as unobservable inputs in which little or no market data exists, therefore requiring an entity to develop its own assumptions. As of March 31, 2020, the Company held certain items that are required to be measured at fair value on a recurring basis. These included cash equivalents, short-term investments (primarily treasury bills and certificates of deposit), interest rate derivative contracts, fuel derivative contracts, and available-for-sale securities. The majority of the Company’s short-term investments consist of instruments classified as Level 1. However, the Company has certificates of deposit, commercial paper, and time deposits that are classified as Level 2, due to the fact that the fair value for these instruments is determined utilizing observable inputs in non-active markets. Other available-for-sale securities primarily consist of investments associated with the Company’s excess benefit plan. The Company’s fuel and interest rate derivative instruments consist of over-the-counter contracts, which are not traded on a public exchange. Fuel derivative instruments currently consist solely of option contracts, whereas interest rate derivatives consist solely of swap agreements. See Note 4 for further information on the Company’s derivative instruments and hedging activities. The fair values of swap contracts are determined based on inputs that are readily available in public markets or can be derived from information available in publicly quoted markets. Therefore, the Company has categorized these swap contracts as Level 2. The Company’s Treasury Department, which reports to the Chief Financial Officer, determines the value of option contracts utilizing an option pricing model based on inputs that are either readily available in public markets, can be derived from information available in publicly quoted markets, or are provided by financial institutions that trade these contracts. The option pricing model used by the Company is an industry standard model for valuing options and is the same model used by the broker/dealer community (i.e., the Company’s counterparties). The inputs to this option pricing model are the option strike price, underlying price, risk free rate of interest, time to expiration, and volatility. Because certain inputs used to determine the fair value of option contracts are unobservable (principally implied volatility), the Company has categorized these option contracts as Level 3. Volatility information is obtained from external sources, but is analyzed by the Company for reasonableness and compared to similar information received from other external sources. The fair value of option contracts considers both the intrinsic value and any remaining time value associated with those derivatives that have not yet settled. The Company also considers counterparty credit risk and its own credit risk in its determination of all estimated fair values. To validate the reasonableness of the Company’s option pricing model, on a monthly basis, the Company compares its option valuations to third party valuations. If any significant differences were to be noted, they would be researched in order to determine the reason. However, historically, no significant differences have been noted. The Company has consistently applied these valuation techniques in all periods presented and believes it has obtained the most accurate information available for the types of derivative contracts it holds.
New Accounting Pronouncements	On December 18, 2019, the Financial Accounting Standards Board (the "FASB") issued Accounting Standards Update ("ASU") No. 2019-12, Income Taxes (Topic 740): Simplifying the Accounting for Income Taxes. This new standard eliminates certain exceptions in Accounting Standards Codification ("ASC") 740 related to the approach for intraperiod tax allocation, the methodology for calculating income taxes in an interim period, and the recognition of deferred tax liabilities for outside basis differences. It also clarifies and simplifies other aspects of the accounting for income taxes. This standard is effective for fiscal years, and interim periods within those years, beginning after December 15, 2020, with early adoption permitted in any interim period within that year. The Company elected to early adopt this standard as of January 1, 2020. The most significant impact to the Company is the removal of a limit on the tax benefit recognized on pre-tax losses in interim periods. However, the early adoption as of January 1, 2020, did not have an impact on the Company's financial statements or disclosures for first quarter 2020. On August 29, 2018, the FASB issued ASU No. 2018-15, Intangibles—Goodwill and Other—Internal-Use Software. This standard requires a customer in a cloud computing arrangement that is a service contract to follow the internal-use software guidance in ASC 350-40, Accounting for Internal-Use Software, to determine which implementation costs to (i) capitalize as assets and amortize over the term of the hosting arrangement or (ii) expense as incurred. This standard is effective for public business entities in fiscal years beginning after December 15, 2019, and the standard was adopted and applied prospectively by the Company as of January 1, 2020, but it did not have a significant impact on the Company's financial statements and disclosures. On August 28, 2018, the FASB issued ASU No. 2018-13, Fair Value Measurement. This standard is effective for public business entities in fiscal years beginning after December 15, 2019, and for interim periods within those fiscal years. This standard requires changes to the disclosure requirements for fair value measurements for certain Level 3 items, and specifies that some of the changes must be applied prospectively, while others should be applied retrospectively. The Company adopted the standard as of January 1, 2020, but it did not have a significant impact on the Company's financial statements or disclosures. See Note 9 for further information on the Company's fair value measurements. On January 26, 2017, the FASB issued ASU No. 2017-04, Simplifying the Test for Goodwill Impairment. The new standard eliminates Step 2 from the goodwill impairment test. An entity should recognize a goodwill impairment charge for the amount by which the carrying amount exceeds the reporting unit's fair value. This standard is effective for public business entities in fiscal years beginning after December 15, 2019, and the standard was adopted and applied prospectively by the Company as of January 1, 2020, but it did not have a significant impact on the Company's financial statements and disclosures. On June 16, 2016, the FASB issued ASU No. 2016-13, Measurement of Credit Losses on Financial Instruments. The new standard requires the use of an “expected loss” model on certain types of financial instruments. The standard also amends the impairment model for available-for-sale debt securities and requires estimated credit losses to be recorded as allowances instead of reductions to amortized cost of the securities. This standard is effective for public business entities in fiscal years beginning after December 15, 2019, and the standard was adopted and applied prospectively by the Company as of January 1, 2020, but it did not have a significant impact on the Company's financial statements and disclosures.
Revenue Recognition	Spoilage estimates are based on the Company's Customers' historical travel behavior as well as assumptions about the Customers' future travel behavior. Assumptions used to generate spoilage estimates can be impacted by several factors including, but not limited to: fare increases, fare sales, changes to the Company's ticketing policies, changes to the Company’s refund, exchange, and unused funds policies, seat availability, and economic factors. Given the unprecedented amount of first quarter 2020 Customer flight cancellations and the amount of travel funds provided, the Company expects additional variability in the amount of spoilage revenue recorded in future periods, as the estimates of the portion of those funds that will expire unused may differ from historical experience. The Company has a co-branded credit card agreement (the “Agreement”) with Chase Bank USA, N.A. (“Chase”), through which the Company sells loyalty points and certain marketing components, which consist of the use of Southwest Airlines’ brand and access to Rapid Rewards Member lists, licensing and advertising elements, and the use of the Company’s resource team. The Company recognized revenue related to the marketing, advertising, and other travel-related benefits of the revenue associated with various loyalty partner agreements including, but not limited to, the Agreement with Chase, within Other operating revenues.