Basis of Presentation (Policies)	9 Months Ended
Basis of Presentation (Policies)	Sep. 30, 2017
Accounting Policies [Abstract]
Basis of Presentation	The unaudited Condensed Consolidated Financial Statements for the interim periods ended September 30, 2017 and 2016 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, natural disasters, 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, the periodic volatility of commodities used by the Company for hedging jet fuel, and the requirements related to hedge accounting, have created, and may continue to create, significant volatility in the Company's financial results. See Note 3 for further information on fuel and the Company's hedging program. Operating results for the three and nine months ended September 30, 2017, are not necessarily indicative of the results that may be expected for future quarters or for the year ended December 31, 2017. For further information, refer to the Consolidated Financial Statements and footnotes thereto included in the Southwest Airlines Co. Annual Report on Form 10-K for the year ended December 31, 2016.
Derivatives	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. For the Company’s interest rate swap agreements that do not qualify for the "shortcut" method of accounting, ineffectiveness is required to be measured at each reporting period. The ineffectiveness associated with all of the Company’s interest rate swap agreements for all periods presented was not material. Upon proper qualification, the Company accounts for its fuel derivative instruments as cash flow hedges. Generally, utilizing hedge accounting, all periodic changes in fair value of the derivatives designated as hedges that are considered to be effective are recorded in Accumulated other comprehensive income (loss) ("AOCI") until the underlying jet fuel is consumed. See Note 4. The Company’s results are subject to the possibility that periodic changes will not be effective, as defined, or that the derivatives will no longer qualify for hedge accounting. Ineffectiveness results when the change in the fair value of the derivative instrument exceeds the change in the value of the Company’s expected future cash outlay to purchase and consume jet fuel. To the extent that the periodic changes in the fair value of the derivatives are ineffective, the ineffective portion is recorded to Other (gains) losses, net, in the unaudited Condensed Consolidated Statement of Comprehensive Income in the period of the change. Likewise, if a hedge ceases to qualify for hedge accounting, any change in the fair value of derivative instruments since the last reporting period is recorded to Other (gains) losses, net, in the unaudited Condensed Consolidated Statement of Comprehensive Income 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. 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. The Company did not have any such situations occur during 2016, or during the nine months ended September 30, 2017.
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 September 30, 2017, 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 Eurodollar 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 include swaps, as well as different types of option contracts, whereas interest rate derivatives consist solely of swap agreements. See Note 3 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 August 28, 2017, the Financial Accounting Standards Board (the "FASB") issued Accounting Standards Update ("ASU") No. 2017-12, Targeted Improvements to Accounting for Hedging Activities. The standard amends the hedge accounting model to enable entities to better portray the economics of their risk management activities in the financial statements and enhance the transparency and understandability of hedge results. The amendments also simplify the application of hedge accounting in certain situations. This ASU is effective for fiscal years, and interim periods within those years, beginning after December 15, 2018, with early adoption permitted in any interim or annual period. The most significant impacts of this ASU on the Company's accounting will be the elimination of ineffectiveness for all cash flow hedges in a hedging relationship, as well as a change in classification of premium expense associated with option contracts. Currently, such premium expense for the Company's fuel hedges is reflected as a component of Other (gains) losses, net, in the Condensed Consolidated Statement of Income, but under the new ASU will be reflected as a component of the line item to which the hedge relates, which is Fuel and oil expense. The Company is currently considering early adoption of the ASU as of January 1, 2018. On March 10, 2017, the FASB issued ASU No. 2017-07, Improving the Presentation of Net Periodic Pension Cost and Net Periodic Postretirement Benefit Cost. The standard requires employers to present the service cost component of the net periodic benefit cost in the same income statement line item as other employee compensation costs arising from services rendered during the period. The other components of net benefit cost, including amortization of prior service cost/credit, and settlement and curtailment effects, are to be included in nonoperating expenses. This ASU is effective for fiscal years, and interim periods within those years, beginning after December 15, 2017. The Company does not expect this to have a material impact on Operating income and expects this to have no impact on Net income. The Company will adopt this guidance as of January 1, 2018. On January 26, 2017, the FASB issued ASU No. 2017-04, Simplifying the Test for Goodwill Impairment. The standard simplifies the accounting for goodwill impairment by removing Step 2 of the goodwill impairment test (as defined by the FASB), which requires a hypothetical purchase price allocation (implied fair value of goodwill) to measure impairment loss. This ASU is effective for fiscal years, and interim periods within those years, beginning after December 15, 2019, with early adoption permitted. The Company does not expect this ASU to have a significant impact on its financial statement presentation or results. On February 25, 2016, the FASB issued ASU No. 2016-02, Leases. The standard is effective for fiscal years, and interim periods within those years, beginning after December 15, 2018, with early adoption permitted. The guidance requires lessees to recognize a right-of-use asset and a lease liability on the balance sheet for all leases (with the exception of short-term leases) at the lease commencement date and recognize expenses on the income statement in a similar manner to the current guidance in Accounting Standards Codification 840, Leases. The lease liability will be measured at the present value of the unpaid lease payments and the right-of-use asset will be derived from the calculation of the lease liability. Lease payments will include fixed and in-substance fixed payments, variable payments based on an index or rate, reasonably certain purchase options, termination penalties, fees paid by the lessee to the owners of a special-purpose entity for restructuring the transaction, and probable amounts the lessee will owe under a residual value guarantee. Lease payments will not include variable lease payments other than those that depend on an index or rate, any guarantee by the lessee of the lessor’s debt, or any amount allocated to non-lease components. The Company has formed a project team to evaluate and implement the standard, and currently believes the most significant impact of this ASU on its accounting will be the balance sheet impact of its aircraft operating leases, which will significantly increase assets and liabilities. As of September 30, 2017, the Company had 53 leased aircraft under operating leases and also had another 76 aircraft under operating leases that are being subleased to another airline. As of September 30, 2017, the net present value of future rents for those aircraft was approximately $1.0 billion. This amount only includes contractual payments due to lessors, and does not consider certain items that the standard requires to be assessed in determining the final asset and liability to be reflected on the Company's balance sheet, such as lease renewal options and potential impairments, nor does it consider the sublease income that is due from third parties. The Company also has operating leases related to terminal operations space and other real estate leases. Although the real estate leases will also have a substantial impact to the balance sheet, the Company does not expect the leases related to terminal operations space to have a significant impact since variable lease payments, other than those based on an index or rate, are excluded from the measurement of the lease liability. The Company also does not expect the adoption of this ASU to impact any of its existing debt covenants. In addition, the standard eliminates the current build-to-suit lease accounting guidance and could result in derecognition of build-to-suit assets and liabilities that remained on the balance sheet after the end of the construction period. The underlying leases for these facilities will be subject to evaluation under the new standard. See Note 7 for further information on the Company’s build-to-suit projects. The Company anticipates utilizing the modified retrospective transition approach to adopt the standard, which requires application of the new guidance for all periods presented with an option to use certain practical expedients. The Company currently plans to adopt the standard as of January 1, 2018, pending successful implementation of a third-party lease accounting software and completion of remaining administrative tasks. The Company is continuing to evaluate the new guidance and plans to provide additional information in its 2017 10-K. On May 28, 2014, the FASB issued ASU No. 2014-09, Revenue from Contracts with Customers. Following the FASB's finalization of a one year deferral of this standard, the ASU is now effective for fiscal years, and interim periods within those years, beginning after December 15, 2017. The Company has formed a project team to evaluate and work to implement the standard, and currently believes the most significant impact of this ASU on its accounting will be the elimination of the incremental cost method for frequent flyer accounting, which will require the Company to re-value its liabilities associated with Customer flight points with a relative fair value approach, resulting in a significant increase in the liabilities. The Company's liabilities associated with these flight points were $64 million at September 30, 2017, and the Company currently estimates that applying a relative fair value approach would increase the liabilities by approximately 20 to 25 times that value, depending on various assumptions made at the time of measurement. The adoption of the new standard is also expected to result in different income statement classification for certain types of revenues which are currently classified as Other revenues, but under the new ASU would be included in Passenger revenues. Based on the Company's full year 2016 results, the amount to be reclassified would have been approximately $600 million. However, the estimated impact of this ASU would not have had a material impact on Operating revenues and would not have impacted any of its existing debt covenants. The Company currently anticipates utilizing the full retrospective method of adoption allowed by the standard, in order to provide for comparative results in all periods presented, and will adopt the standard as of January 1, 2018. The Company is continuing to evaluate the new guidance both internally and through its participation in an industry working group, and plans to continue to provide relevant and material information prior to adoption. The Company is in the process of completing its analysis of information necessary to recast prior period results, however it does not believe there are any remaining significant implementation topics associated with the adoption of this ASU that have not yet been addressed.