| Summary of Significant Accounting Policies (Policies) | 12 Months Ended |
| Dec. 31, 2018 |
| Accounting Policies [Abstract] | |
| New Accounting Pronouncements, Policy | On August 28, 2017, the FASB issued the New Hedging Standard. The New Hedging 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 New Hedging Standard also simplifies the application of hedge accounting in certain situations. The New Hedging Standard 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 Company elected to early adopt the New Hedging Standard as of January 1, 2018, utilizing a modified retrospective approach, as required. The most significant impacts of the New Hedging Standard on the Company's accounting are the elimination of the requirement to separately measure and record ineffectiveness for all cash flow hedges in a hedging relationship, as well as a change in classification of premium expense associated with option contracts. Such premium expense for the Company's fuel hedges was previously reflected as a component of Other (gains) losses, net, in the Consolidated Statement of Income, but under the New Hedging Standard is reflected as a component of the line item to which the hedge relates, which is Fuel and oil expense. As such, premium expense for the years ended December 31, 2017 and 2016 , has been reclassified in order to be comparative with current period results in the accompanying Consolidated Statement of Income. The impact of the cumulative effect of the adjustment to move the reporting of ineffectiveness as of January 1, 2018, to AOCI from Retained earnings, was a $20 million loss, net of taxes. The adoption and resulting reclassification had no impact on the Company's Net income, earnings per share, or cash flows. As a result of the adoption of the New Hedging Standard, however, the Company incurred no gains or losses due to ineffectiveness in Other (gains) losses, net, in the Consolidated Statement of Income, during 2018. See Note 10 for further information and for further details on gains or losses recorded due to ineffectiveness during 2017. On March 10, 2017, the FASB issued the New Retirement Standard. The New Retirement 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. As required by the New Retirement Standard, the Company adopted this guidance retrospectively as of January 1, 2018, using a practical expedient which permitted the Company to use the amounts disclosed in its pension and other postretirement benefit plan note for the prior comparative periods as the estimation basis for applying the retrospective presentation requirements. As such, the Company reclassified $14 million and $ 12 million of Salaries, wages, and benefits expense to Other (gains) and losses under the New Retirement Standard in the accompanying Consolidated Statement of Income for the years ended December 31, 2017 and 2016 , respectively. The adoption and resulting reclassification had no impact on the Company's Net income, earnings per share, or cash flows. On February 25, 2016, the FASB issued ASU No. 2016-02, Leases (the "New Lease Standard"). The New Lease Standard is effective for fiscal years, and interim periods within those years, beginning after December 15, 2018, with early adoption permitted. The New Lease Standard 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 ASC 840, Leases ("ASC 840"). The lease liability will be measured as 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 established a project team to evaluate and implement the New Lease Standard. The Company currently believes the most significant impact of the New Lease Standard on its accounting will be the balance sheet impact of its aircraft operating leases, which will significantly increase assets and liabilities. As of December 31, 2018 , the Company had 51 leased aircraft under operating leases in its active fleet and also had another 73 aircraft under operating leases that are being subleased to another airline. 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 the New Lease Standard to impact any of its existing debt covenants. In addition, the New Lease Standard eliminates the current build-to-suit lease accounting guidance and is expected to result in derecognition of build-to-suit assets and liabilities that remained on the balance sheet after the end of the construction period, including the related deferred taxes. See Note 4 for further information on the Company’s build-to-suit projects. However, given the Company's guarantee associated with the bonds issued to fund the Dallas Love Field Modernization Program (the "LFMP"), the Company believes that the remaining debt service amounts as of the adoption date would be considered a minimum rental payment under the New Lease Standard, and therefore will be recorded as a lease liability on the balance sheet and will be reduced through future debt service payments made in 2019 and beyond. The underlying leases for all of these facilities will be subject to evaluation under the New Lease Standard. The Company plans to elect the package of practical expedients available under the transition provisions of the New Lease Standard, including (i) not reassessing whether expired or existing contracts contain leases, (ii) lease classification, and (iii) not revaluing initial direct costs for existing leases. Also, the Company plans to elect the practical expedient which will allow aggregation of non-lease components with the related lease components when evaluating accounting treatment. Lastly, the Company currently plans to apply the modified retrospective adoption method, utilizing the simplified transition option available in the New Lease Standard, which allows entities to continue to apply the legacy guidance in ASC 840, including its disclosure requirements, in the comparative periods presented in the year of adoption. The Company will adopt the New Lease Standard on January 1, 2019. The expected impact of applying the New Lease Standard effective as of January 1, 2019, to the Company’s results of operations and cash flows is not expected to be significant. The expected major impacts to the balance sheet will be 1) the removal of approximately $1.5 billion in Assets constructed for others, net, and related Construction obligations, and 2) the addition of approximately $1.4 billion in Operating lease right of use assets and lease liabilities, which includes approximately $700 million from operating lease aircraft, approximately $450 million from the Company’s remaining obligations associated with the LFMP bonds, and approximately $220 million from other operating leases. On May 28, 2014, the FASB issued the New Revenue Standard, also referred to as ASC 606, Revenue From Contracts With Customers ("ASC 606"), which replaces numerous revenue recognition requirements in GAAP, including industry-specific requirements, and provides companies with a single revenue recognition model for recognizing revenue from contracts with Customers. The New Revenue Standard establishes a five-step model whereby revenue is recognized as performance obligations within a contract are satisfied in an amount that reflects the consideration the Company expects to receive in exchange for satisfaction of those performance obligations, or standalone selling price. The New Revenue Standard also requires new, expanded disclosures regarding revenue recognition. See Note 5 for further information. The Company adopted the provisions of the New Revenue Standard effective January 1, 2018, using the full retrospective method. As such, results for the years ended December 31, 2017 and 2016 , have been recast under the New Revenue Standard in order to be comparative with current period results in the accompanying Consolidated Statements of Income and Cash Flows. The amounts in the accompanying Consolidated Balance Sheet as of December 31, 2017, have also been recast. The most significant impact of the New Revenue Standard relates to the accounting for the Company’s loyalty program. The New Revenue Standard eliminated the incremental cost method for flight points awarded, which was previously allowed in prior accounting guidance. The Company now accounts for the revenue and liability for loyalty points earned through flight activity using a relative fair value approach. The New Revenue Standard also resulted in different income statement classification for certain types of revenues (primarily ancillary revenues) which were previously classified as Other revenues, but under the New Revenue Standard are included in Passenger revenues, and certain expenses, which were previously classified as Other operating expenses, but under the New Revenue Standard are offset against Passenger revenues. The following table provides the impact of applying the New Revenue Standard to the Company’s previously reported balances as of December 31, 2017: Balance as of December 31, 2017 (in millions) As Reported New Revenue Standard As Recast Accrued liabilities $ 1,777 $ (77 ) $ 1,700 Air traffic liability 3,460 35 3,495 Air traffic liability - noncurrent — 1,070 1,070 Deferred income taxes 2,358 (239 ) 2,119 Retained earnings 14,621 (789 ) 13,832 The impacts of applying the New Revenue Standard, the New Retirement Standard, and the New Hedging Standard to the Company’s Consolidated Statement of Income for the years ended December 31, 2017 and 2016 , are as follows (amounts may not recalculate due to rounding): Year ended December 31, 2017 (in millions), except per share amounts As Reported New Revenue Standard New Retirement Standard New Hedging Standard As Recast Passenger revenue $ 19,141 $ 622 $ — $ — $ 19,763 Other revenue 1,857 (647 ) — — 1,210 Salaries, wages, and benefits 7,319 — (14 ) — 7,305 Fuel and oil expense 3,940 — — 136 4,076 Other operating expenses 2,886 (39 ) — — 2,847 Other (gains) losses, net 234 — 14 (136 ) 112 Provision for income taxes (237 ) 145 — — (92 ) Net income 3,488 (131 ) — — 3,357 Net income per share, basic 5.80 (0.22 ) — — 5.58 Net income per share, diluted 5.79 (0.22 ) — — 5.57 Year ended December 31, 2016 (in millions), except per share amounts As Reported New Revenue Standard New Retirement Standard New Hedging Standard As Recast Passenger revenue $ 18,594 $ 474 $ — $ — $ 19,068 Other revenue 1,660 (610 ) — — 1,050 Salaries, wages, and benefits 6,798 — (12 ) — 6,786 Fuel and oil expense 3,647 — — 154 3,801 Other operating expenses 2,743 (40 ) — — 2,703 Other (gains) losses, net 162 — 12 (154 ) 21 Provision for income taxes 1,303 (36 ) — — 1,267 Net income 2,244 (60 ) — — 2,183 Net income per share, basic 3.58 (0.10 ) — — 3.48 Net income per share, diluted 3.55 (0.10 ) — — 3.45 The impacts of applying the New Revenue Standard to the Company’s Consolidated Statement of Cash Flows for the years ended December 31, 2017 and 2016 , are as follows (amounts may not recalculate due to rounding): Year ended December 31, 2017 (in millions) As Reported New Revenue Standard As Recast Net income $ 3,488 $ (131 ) $ 3,357 Deferred income taxes (1,212 ) 145 (1,066 ) Changes in certain assets and liabilities 227 (14 ) 212 Net cash provided by operating activities 3,929 — 3,929 Year ended December 31, 2016 (in millions) As Reported New Revenue Standard As Recast Net income $ 2,244 $ (60 ) $ 2,183 Deferred income taxes 455 (36 ) 419 Changes in certain assets and liabilities 182 96 279 Net cash provided by operating activities 4,293 — 4,293 |
| Basis of Presentation | Basis of Presentation Southwest Airlines Co. (the "Company") operates Southwest Airlines, a major domestic airline. The Consolidated Financial Statements include the accounts of the Company and its wholly owned subsidiaries, which include AirTran Holdings, LLC, the successor to AirTran Holdings, Inc. ("AirTran Holdings"), the former parent company of AirTran Airways, Inc. ("AirTran Airways"). The accompanying Consolidated Financial Statements include the results of operations and cash flows for all periods presented and all significant inter-entity balances and transactions have been eliminated. The preparation of financial statements in conformity with generally accepted accounting principles in the United States ("GAAP") requires management to make estimates and assumptions that affect the amounts reported in the financial statements and accompanying notes. Actual results could differ from these estimates. Effective as of January 1, 2018, the Company adopted Accounting Standards Update ("ASU") No. 2014-09, Revenue from Contracts with Customers (the "New Revenue Standard"), ASU No. 2017-07, Improving the Presentation of Net Periodic Pension Cost and Net Periodic Postretirement Benefit Cost (the "New Retirement Standard"), and ASU No. 2017-12, Targeted Improvements to Accounting for Hedging Activities (the "New Hedging Standard"). All amounts and disclosures set forth in this Form 10-K reflect the adoption of these ASUs. See Note 2 for further information. The Company reclassified $198 million and $229 million from Aircraft rentals to Other operating expenses in the Consolidated Statement of Income for the years ended December 31, 2017 and 2016 , respectively, to be comparative with the current period's presentation. Aircraft rentals expense included in Other operating expenses for the year ended December 31, 2018 , was $161 million . This reclassification had no impact on Operating income, Net income, the Consolidated Balance Sheet, or the Consolidated Statement of Cash Flows. |
| Cash and cash equivalents | Cash and Cash Equivalents Cash in excess of that necessary for operating requirements is invested in short-term, highly liquid, income-producing investments. Investments with original maturities of three months or less when purchased are classified as cash and cash equivalents, which primarily consist of certificates of deposit, money market funds, and investment grade commercial paper issued by major corporations and financial institutions. Cash and cash equivalents are stated at cost, which approximates fair value. As of December 31, 2018 , no cash collateral deposits were provided by or held by the Company from its fuel hedge counterparties, and no cash collateral deposits were held by or provided by the Company to its interest rate hedge counterparties. As of December 31, 2017 , $15 million in cash collateral deposits were held by the Company from its fuel hedge counterparties, and no cash collateral deposits were held by or provided by the Company to its interest rate hedge counterparties. Cash collateral amounts provided or held associated with fuel and interest rate derivative instruments are not restricted in any way and earn interest income at an agreed upon rate that approximates the rates earned on short-term securities issued by the U.S. Government. Depending on the fair value of the Company’s fuel and interest rate derivative instruments, the amounts of collateral deposits held or provided at any point in time can fluctuate significantly. See Note 10 for further information on these collateral deposits and fuel derivative instruments. |
| Short-term and noncurrent investments | Short-term and Noncurrent Investments Short-term investments consist of investments with original maturities of greater than three months but less than twelve months when purchased. These are primarily short-term securities issued by the U.S. Government and certificates of deposit issued by domestic banks. All of these investments are classified as available-for-sale securities and are stated at fair value, which approximates cost. For all short-term investments, at each reset period or upon reinvestment, the Company accounts for the transaction as Proceeds from sales of short-term investments for the security relinquished, and Purchases of short-investments for the security purchased, in the accompanying Consolidated Statement of Cash Flows. Unrealized gains and losses, net of tax, if any, are recognized in Accumulated other comprehensive income (loss) ("AOCI") in the accompanying Consolidated Balance Sheet. Realized net gains and losses on specific investments, if any, are reflected in Interest income in the accompanying Consolidated Statement of Income. Both unrealized and realized gains and/or losses associated with investments were immaterial for all years presented. Noncurrent investments consist of investments with maturities of greater than twelve months. Noncurrent investments are included as a component of Other assets in the Consolidated Balance Sheet. |
| Accounts and other receivables | Accounts and Other Receivables Accounts and other receivables are carried at cost. They primarily consist of amounts due from credit card companies associated with sales of tickets for future travel, and amounts due from business partners in the Company’s loyalty program. The allowance for doubtful accounts was immaterial at December 31, 2018 and 2017 . In addition, the provision for doubtful accounts and write-offs for 2018 , 2017 , and 2016 were each immaterial. |
| Inventories | Inventories Inventories primarily consist of aircraft fuel, flight equipment expendable parts, materials, and supplies. All of these items are carried at average cost, less an allowance for obsolescence. These items are generally charged to expense when issued for use. The reserve for obsolescence was $2 million and $45 million at December 31, 2018 , and 2017 , respectively. In addition, the Company’s provision for obsolescence and write-offs for 2018 , 2017 , and 2016 were each immaterial. |
| Property and equipment | Property and Equipment Property and equipment is stated at cost. Capital expenditures include payments made for aircraft, other flight equipment, purchase deposits related to future aircraft deliveries, airport and other facility construction projects, and ground and other property and equipment. Depreciation is provided by the straight-line method to estimated residual values over periods of approximately 25 years for flight equipment, 5 to 30 years for ground property and equipment, and 5 to 30 years, or the expected term of the Company's lease if shorter, for Assets constructed for others, once the asset is placed in service. Residual values estimated for aircraft are approximately 15 percent , for ground property and equipment generally range from 0 to 10 percent , and for Assets constructed for others range from 17 to 75 percent . Property under capital leases and related obligations are initially recorded at an amount equal to the present value of future minimum lease payments computed on the basis of the Company’s incremental borrowing rate or, when known, the interest rate implicit in the lease. Amortization of property under capital leases is on a straight-line basis over the lease term and is included in Depreciation and amortization expense. Leasehold improvements generally are amortized on a straight-line basis over the shorter of the estimated useful life of the improvement or the remaining term of the lease. Assets constructed for others consists of airport improvement projects in which the Company is considered the accounting owner of the facilities. See Note 4 for further information. During first quarter 2016, the Company made the decision to further simplify its operations and accelerate the retirement of its less-efficient Boeing 737-300 ("Classic") fleet. In September 2017, the Company retired the remaining 61 Classic aircraft as part of this accelerated retirement schedule. This change in retirement dates was considered a change in estimate and was accounted for on a prospective basis as of the dates the decisions were finalized. Therefore, the Company recorded accelerated depreciation expense over the remainder of the useful lives for each Classic aircraft and related parts. See Note 7 for further information regarding the Company's aircraft fleet. The impacts on expense and earnings from the accelerated depreciation were as follows: (in millions, except per share amounts) Year ended December 31, 2017 Year ended December 31, 2016 Depreciation and amortization expense $ 21 $ 123 Net income * $ (19 ) $ (66 ) Net income per basic share $ (0.03 ) $ (0.11 ) Net income per diluted share $ (0.03 ) $ (0.10 ) * net of profitsharing benefit and income taxes The Company evaluates its long-lived assets used in operations for impairment when events and circumstances indicate that the undiscounted cash flows to be generated by that asset are less than the carrying amounts of the asset and may not be recoverable. Factors that would indicate potential impairment include, but are not limited to, significant decreases in the market value of the long-lived asset(s), a significant change in the long-lived asset’s physical condition, and operating or cash flow losses associated with the use of the long-lived asset. If an asset is deemed to be impaired, an impairment loss is recorded for the excess of the asset book value in relation to its estimated fair value. |
| Aircraft and engine maintenance | Aircraft and Engine Maintenance The cost of scheduled inspections and repairs and routine maintenance costs for all aircraft and engines are charged to Maintenance materials and repairs expense within the accompanying Consolidated Statement of Income as incurred. The Company has maintenance agreements related to certain of its aircraft engines with external service providers, including a "power-by-the-hour" agreement associated with its Boeing 737-700 fleet. Under these agreements, which the Company has determined effectively transfer the risk and create an obligation associated with the maintenance on such engines to the counterparty, expense is recorded commensurate with each hour flown on an engine. In situations where the payments to the counterparty do not sufficiently match the level of services received during the period, expense is recorded on a straight-line basis over the term of the agreement based on the Company's best estimate of expected future aircraft utilization. For its engine maintenance contracts that do not transfer risk to the service provider, the Company records expense on a time and materials basis when an engine repair event takes place. Modifications that significantly enhance the operating performance or extend the useful lives of aircraft or engines are capitalized and amortized over the remaining life of the asset. |
| Goodwill and intangible assets | Goodwill and Intangible Assets The Company applies a fair value based impairment test to the carrying value of goodwill and indefinite-lived intangible assets annually on October 1st, or more frequently if certain events or circumstances indicate that an impairment loss may have been incurred. The Company assesses the value of goodwill and indefinite-lived assets under either a qualitative or quantitative approach. Under a qualitative approach, the Company considers various market factors, including applicable key assumptions listed below. These factors are analyzed to determine if events and circumstances could reasonably have affected the fair value of goodwill and indefinite-lived intangible assets. If the Company determines that it is more likely than not that an indefinite-lived intangible asset is impaired, the quantitative approach is used to assess the asset’s implied fair value and the amount of the impairment. Under a quantitative approach, the implied fair value of the Company's identifiable assets and liabilities is calculated based on key assumptions. If the Company assets' carrying value exceeds the fair value calculated using the quantitative approach, an impairment charge is recorded for the difference in fair value and carrying value. During 2016, the Company recorded a $21 million impairment charge associated with leased slots at Newark Liberty International Airport as a result of the FAA announcement, in April 2016, that this airport was being changed to a Level 2 schedule-facilitated airport from its previous designation as Level 3. This impairment loss was reflected in Other operating expenses within the accompanying Consolidated Statement of Income. The Company does not believe this FAA decision is indicative of a similar decision being made at the Company's other slot-controlled airports, Washington Reagan and New York LaGuardia. The following table is a summary of the Company’s intangible assets, which are included as a component of Other assets in the Company's Consolidated Balance Sheet, as of December 31, 2018 and 2017 : Year ended December 31, 2018 Year ended December 31, 2017 (in millions) Weighted-average useful life (in years) Gross carrying amount Accumulated amortization Gross carrying amount Accumulated Amortization Customer relationships/marketing agreements 10 $ 27 $ 25 $ 27 $ 23 Owned domestic slots (a) Indefinite 295 n/a 295 n/a Gate leasehold rights (a) 15 180 78 180 66 Total 14 $ 502 $ 103 $ 502 $ 89 (a) Intangible assets primarily consist of acquired leasehold rights to certain airport owned gates, takeoff and landing slots (a "slot" is the right of an air carrier, pursuant to regulations of the FAA, to operate a takeoff or landing at a specific time at certain airports) at certain domestic slot-controlled airports, and certain intangible assets acquired. The Company's definite lived assets are amortized on a straight-line basis over the useful life of the asset. The aggregate amortization expense for 2018 , 2017 , and 2016 was $16 million , $13 million , and $17 million , respectively. Estimated aggregate amortization expense for the five succeeding years and thereafter is as follows: 2019 – $13 million , 2020 – $12 million , 2021 – $12 million , 2022 – $12 million , 2023 – $12 million , and thereafter – $45 million . |
| Revenue recognition | Revenue Recognition Tickets sold are initially deferred as Air traffic liability. Passenger revenue is recognized and Air traffic liability is reduced when transportation is provided. Air traffic liability primarily represents tickets sold for future travel dates and funds that are past flight date and remain unused as well as a portion of the Company's liability associated with its loyalty program. The majority of the Company’s tickets sold are nonrefundable. Refundable tickets that are sold but not flown on the travel date can be reused for another flight, up to a year from the date of sale, or refunded, subject to certain conditions. Based on the Company's revenue recognition policy, revenue is recorded at the flight date for a Customer who does not change his/her itinerary and loses his/her funds as the Company has then fulfilled its performance obligation. Amounts collected from passengers for ancillary service fees are also recognized when the service is provided, which is typically the flight date. Revenue from the estimated spoilage of tickets (including partial tickets) is recorded once the flight date has passed in proportion to the pattern of flights taken by the Customer, which approximates the average period over which the population of Rapid Reward Members redeem their points. Initial spoilage estimates are routinely adjusted and ultimately finalized once the tickets expire, which is typically twelve months after the original purchase date. See Note 5 for further information. Approximately $566 million , approximately $489 million , and approximately $383 million of the Company's Operating revenues in 2018 , 2017 , and 2016 , respectively, were attributable to foreign operations. The remainder of the Company's Operating revenues, approximately $21.4 billion , approximately $20.7 billion , and approximately $20.0 billion in 2018 , 2017 , and 2016 , respectively, were attributable to domestic operations. The balance in Air traffic liability – passenger travel and ancillary passenger services also includes unused funds that are available for use by Customers that are not currently associated with a ticket, but represent funds effectively refunded and made available for use to purchase a ticket for a flight that occurs prior to their expiration. These funds are typically created as a result of a prior ticket cancellation or exchange. These performance obligations are expected to have a duration of twelve months or less; therefore, the Company has elected the provision within ASC 606 to not disclose the amount of the remaining transaction price and its expected timing of recognition for passenger tickets. Recognition of revenue associated with the Company’s loyalty liability can be difficult to predict, as the number of award seats available to members is not currently restricted and they could choose to redeem their points at any time that a seat is available. The performance obligations classified as a current liability related to the Company’s loyalty program were estimated based on expected redemptions utilizing historical redemption patterns, and forecasted flight availability, fares, and coefficients. The entire balance classified as Air traffic liability – noncurrent relates to loyalty points that were estimated to be redeemed in periods beyond 12 months following the representative balance sheet date. The Company expects the majority of loyalty points to be redeemed within two years. The Company is also required to collect certain taxes and fees from Customers on behalf of government agencies and remit these back to the applicable governmental entity on a periodic basis. These taxes and fees include foreign and U.S. federal transportation taxes, federal security charges, and airport passenger facility charges. These items are collected from Customers at the time they purchase their tickets, are excluded from the contract transaction price, and are therefore not included in Passenger revenue. The Company records a liability upon collection from the Customer and relieves the liability when payments are remitted to the applicable governmental agency. All performance obligations related to freight services sold are completed within twelve months or less; therefore, the Company has elected the provision within ASC 606 to not disclose the amount of the remaining transaction price and its expected timing of recognition for freight shipments. Other revenues primarily consist of marketing royalties associated with the Company’s co-branded Chase ® Visa credit card, but also include commissions and advertising associated with Southwest.com ® . All amounts classified as Other revenues are paid monthly, coinciding with the Company fulfilling its deliverables; therefore, the Company has elected the provision within ASC 606 to not disclose the amount of the remaining transaction price and its expected timing of recognition for such services provided. In order to determine the value of each loyalty point, certain assumptions must be made at the time of measurement, which include the following: • Allocation of Passenger Revenue - Revenues from Passengers, related to travel, who also earn Rapid Rewards Points have been allocated between flight (recognized as revenue when transportation is provided) and Rapid Rewards Points (deferred until points are redeemed or spoil) based on each obligation’s relative standalone selling price. The Company utilizes historical earning patterns to assist in this allocation. • Fair Value of Rapid Rewards Points - Determined from the base fare value of tickets which were purchased using prior point redemptions for travel and other products and services, which the Company believes to be indicative of the fair value of points as perceived by Customers and representative of the value of each point at the time of redemption. The Company’s booking site allows a Customer to toggle between fares utilizing either cash or point redemptions, which provides the Customer with an approximation of the equivalent value of their points. The value can differ, however, based on demand, the amount of time prior to the flight, and other factors. The fare mix during the period measured represents a constraint, which could result in the assumptions above changing at the measurement date, as fare classes can have different coefficients used to determine the total loyalty points needed to purchase an award ticket. The mixture of these fare classes and changes in the coefficients used by the Company could cause the fair value per point to increase or decrease. For points that are expected to expire unused, the Company recognizes spoilage in proportion to the pattern of points used by the Customer, which approximates the average period over which the population of Rapid Reward Members redeem their points. The Company utilizes historical behavioral data to develop a predictive statistical model to analyze the amount of spoilage expected for points sold to business partners and earned through flight. The Company continues to evaluate expected spoilage annually and applies appropriate adjustments in the fourth quarter of each year, or other times, if changes in Customer behavior are detected. Changes to spoilage estimates impact revenue recognition prospectively. In most historical periods, the impact of changes in the estimated spoilage rate has not resulted in material changes to revenue recognition. However, due to the size of the Company’s liability for loyalty benefits as a result of the elimination of the incremental cost method of accounting for flight points, changes in Customer behavior and/or expected future redemption patterns could result in more significant variations in Passenger revenue under the New Revenue Standard. These analyses have not resulted in material adjustments in 2018 , 2017 , or 2016 . |
| Loyalty program | Loyalty Program The Company records a liability for the relative fair value of providing free travel under its loyalty program for all points earned from flight activity or sold to companies participating in the Company’s Rapid Rewards loyalty program as business partners that are expected to be redeemed for future travel. The loyalty liability represents performance obligations that will be satisfied when a Rapid Rewards loyalty member redeems points for travel or other goods and services, or upon spoilage of the points. Points earned from flight activity are valued at their relative standalone selling price by applying fair value based on historical redemption patterns. Points earned from business partner activity, which primarily consist of points sold, along with related services, to companies participating in the Rapid Rewards loyalty program, are valued using a relative fair value methodology based on the contractual rate which partners pay to Southwest to award Rapid Rewards points to the business partner’s customers. For points that are expected to expire unused, the Company recognizes spoilage in proportion to the pattern of points used by the Customer, which approximates the average period over which the population of Rapid Reward Members redeem their points. The Company records passenger revenue related to air transportation when the transportation is delivered. The marketing elements are recognized as Other - net revenue when earned. See Note 5 for further information. |
| Advertising | Advertising Advertising costs are charged to expense as incurred. Advertising and promotions expense for the years ended December 31, 2018 , 2017 , and 2016 was $215 million , $224 million , and $232 million , respectively, and is included as a component of Other operating expense in the accompanying Consolidated Statement of Income. |
| Share-based Employee compensation | Share-based Employee Compensation The Company has share-based compensation plans covering certain Employees, including a plan that also covers the Company’s Board of Directors. The Company accounts for share-based compensation based on its grant date fair value. See Note 9 for further information. Outstanding RSUs vest over three years , subject generally to the individual’s continued employment or service. The PBRSUs granted in January 2016 and February 2017 are subject to the Company’s performance with respect to a three-year simple average of Return on Invested Capital, before taxes and excluding special items, for the defined performance period and the individual’s continued employment or service. The PBRSUs granted in January 2018 are subject to the Company’s performance with respect to a three-year simple average of Return on Invested Capital, after taxes and excluding special items, for the defined performance period and the individual’s continued employment or service. The number of PBRSUs vesting on the vesting date will be interpolated based on the Company's Return on Invested Capital performance and ranges from zero PBRSUs to 200 percent of granted PBRSUs. Grants of RSUs result in the creation of a deferred tax asset, which is a temporary difference, until the time the RSU vests. All excess tax benefits and tax deficiencies are recorded through the income statement. Due to the treatment of RSUs for tax purposes, the Company’s effective tax rate from year to year is subject to variability. The Company accounts for share-based compensation utilizing fair value, which is determined on the date of grant for all instruments. |
| Fair Value of Financial Instruments | Financial Derivative Instruments The Company accounts for financial derivative instruments at fair value and applies hedge accounting rules where appropriate. The Company utilizes various derivative instruments, including jet fuel, crude oil, unleaded gasoline, and heating oil-based derivatives, to attempt to reduce the risk of its exposure to jet fuel price increases. These instruments are accounted for as cash flow hedges upon proper qualification. The Company also has interest rate swap agreements to convert a portion of its fixed-rate debt to floating rates and has swap agreements that convert certain floating-rate debt to a fixed-rate. The majority of these interest rate hedges are appropriately designated as either fair value hedges or as cash flow hedges. Since the majority of the Company’s financial derivative instruments are not traded on a market exchange, the Company estimates their fair values. Depending on the type of instrument, the values are determined by the use of present value methods or option value models with assumptions about commodity prices based on those observed in underlying markets. The Company adopted the New Hedging Standard as of January 1, 2018. See Note 2 for further information on this adoption. All cash flows associated with purchasing and selling derivatives are classified as operating cash flows in the Consolidated Statement of Cash Flows, within Changes in certain assets and liabilities. The Company classifies its cash collateral provided to or held from counterparties in a "net" presentation on the Consolidated Balance Sheet against the fair value of the derivative positions with those counterparties. See Note 10 for further information. The significant unobservable input used in the fair value measurement of the Company’s derivative option contracts is implied volatility. Holding other inputs constant, an increase (decrease) in implied volatility would result in a higher (lower) fair value measurement, respectively, for the Company’s derivative option contracts. 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 December 31, 2018 , 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 10 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. |
| Software capitalization | Software Capitalization The Company capitalizes certain internal and external costs related to the acquisition and development of internal use software during the application development stages of projects. The Company amortizes these costs using the straight-line method over the estimated useful life of the software, which is typically five to fifteen years. Costs incurred during the preliminary project or the post-implementation/operation stages of the project are expensed as incurred. Capitalized computer software, included as a component of Ground property and equipment in the accompanying Consolidated Balance Sheet, net of accumulated depreciation, was $674 million and $654 million at December 31, 2018 , and 2017 , respectively. Computer software depreciation expense was $155 million , $168 million , and $111 million for the years ended December 31, 2018 , 2017 , and 2016 , respectively, and is included as a component of Depreciation and amortization expense in the accompanying Consolidated Statement of Income. The Company evaluates internal use software for impairment on a quarterly basis; if it is determined the value of an asset was not recoverable or it qualifies for impairment, a charge will be recorded to write down the software to the lower of its carrying value or fair value. The Company had no significant impairments during 2018 , 2017 , or 2016 . |
| Income taxes | Income Taxes The Company accounts for deferred income taxes utilizing an asset and liability method, whereby deferred tax assets and liabilities are recognized based on the tax effect of temporary differences between the financial statements and the tax basis of assets and liabilities, as measured by current enacted tax rates. The Company also evaluates the need for a valuation allowance to reduce deferred tax assets to estimated recoverable amounts. The Company’s policy for recording interest and penalties associated with uncertain tax positions is to record such items as a component of income before income taxes. Penalties are recorded in Other (gains) losses, net, and interest paid or received is recorded in Interest expense or Interest income, respectively, in the accompanying Consolidated Statement of Income. There were no material amounts recorded for penalties and interest related to uncertain tax positions for all years presented. |
| Concentration risk | Concentration Risk Approximately 83 percent of the Company’s full-time equivalent Employees are unionized and are covered by collective-bargaining agreements. A percentage of the Company's unionized Employees, including its Flight Attendants, Customer Service Agents, Mechanics, Flight Simulator Technicians, and Material Specialists, are in discussions on labor agreements. Those unionized Employee groups in discussions represent approximately 43 percent of the Company’s full-time equivalent Employees as of December 31, 2018 . The Company attempts to minimize its concentration risk with regards to its cash, cash equivalents, and its investment portfolio. This is accomplished by diversifying and limiting amounts among different counterparties, the type of investment, and the amount invested in any individual security or money market fund. To manage risk associated with financial derivative instruments held, the Company selects and will periodically review counterparties based on credit ratings, limits its exposure to a single counterparty, and monitors the market position of the program and its relative market position with each counterparty. The Company also has agreements with counterparties containing early termination rights and/or bilateral collateral provisions whereby security is required if market risk exposure exceeds a specified threshold amount or credit ratings fall below certain levels. Collateral deposits provided to or held from counterparties serve to decrease, but not totally eliminate, the credit risk associated with the Company’s hedging program. See Note 10 for further information. As of December 31, 2018 , the Company operated an all-Boeing fleet, all of which are variations of the Boeing 737. If the Company were unable to acquire additional aircraft or associated aircraft parts from Boeing, or Boeing were unable or unwilling to make timely deliveries of aircraft or associated parts, or to provide adequate support for its products, the Company’s operations would be materially adversely impacted. In addition, the Company would be materially adversely impacted in the event of a mechanical or regulatory issue associated with the Boeing 737 aircraft type, whether as a result of downtime for part or all of the Company’s fleet, increased maintenance costs, or because of a negative perception by the flying public. The Company is also dependent on sole or limited suppliers for aircraft engines and certain other aircraft parts and services and would, therefore, also be materially adversely impacted in the event of the unavailability of, inadequate support for, or a mechanical or regulatory issue associated with, engines and other parts. The Company has historically entered into agreements with some of its co-brand, payment, and loyalty partners that contain exclusivity aspects which place certain confidential restrictions on the Company from entering into certain arrangements with other payment and loyalty partners. These arrangements generally extend for the terms of the agreements, which typically are for five to seven years, but none of which are more than 10 years in length. Some of these agreements automatically renew on an annual basis, unless either party objects to such extension. The Company believes the financial benefits generated by the exclusivity aspects of these arrangements outweigh the risks involved with such agreements. |
| Derivatives | All of the Company's fuel derivative instruments and interest rate swaps are subject to agreements that follow the netting guidance in the applicable accounting standards for derivatives and hedging. The types of derivative instruments the Company has determined are subject to netting requirements in the accompanying Consolidated Balance Sheet are those in which the Company pays or receives cash for transactions with the same counterparty and in the same currency via one net payment or receipt. For cash collateral held by the Company or provided to counterparties, the Company nets such amounts against the fair value of the Company's derivative portfolio by each counterparty. The Company has elected to utilize netting for both its fuel derivative instruments and interest rate swap agreements and also classifies such amounts as either current or noncurrent, based on the net fair value position with each of the Company's counterparties in the Consolidated Balance Sheet. The Company's application of its netting policy associated with cash collateral differs depending on whether its derivative instruments are in a net asset position or a net liability position. If its fuel derivative instruments are in a net asset position with a counterparty, cash collateral amounts held are first netted against current outstanding derivative asset amounts associated with that counterparty until that balance is zero, and then any remainder is applied against the fair value of noncurrent outstanding derivative instruments. If the Company's fuel derivative instruments are in a net liability position with the counterparty, cash collateral amounts provided are first netted against noncurrent outstanding derivative amounts associated with that counterparty until that balance is zero, and then any remainder is applied against the fair value of current outstanding derivative instruments Upon proper qualification, the Company accounts for its fuel derivative instruments as cash flow hedges. The Company adopted the New Hedging Standard as of January 1, 2018. See Note 2 for further information on this adoption. Under the New Hedging Standard, all periodic changes in fair value of the derivatives designated as hedges are recorded in AOCI until the underlying jet fuel is consumed. See Note 12 . Prior to the adoption of the New Hedging Standard, ineffectiveness resulted when the change in the fair value of the derivative instrument exceeded the change in the value of the Company’s expected future cash outlay to purchase and consume jet fuel. Prior to 2018, those expected future cash outlays represented forecasted forward jet fuel prices, which were estimated through utilization of a statistical–based regression equation with data from market forward prices of like commodities. This equation was then adjusted for certain items, such as transportation costs, that are stated in the Company’s fuel purchasing contracts with its vendors. To the extent that the periodic changes in the fair value of the derivatives were ineffective, the ineffective portion was recorded to Other (gains) losses, net, in the Consolidated Statement of Income in the period of the change. 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 Consolidated Statement of 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. 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. The Company did not have any such situations occur during 2018 , 2017 , or 2016 . 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. The New Hedging Standard also addresses targeted improvements to special hedge accounting for interest rate hedges. Though the Company did not make any changes to the accounting for its current interest rate hedges as of the January 2018 adoption date, the New Hedging Standard provides the Company with more opportunities to achieve special hedge accounting for potential interest rate hedges in the future. 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 Accounting pronouncements pertaining to derivative instruments and hedging are complex with stringent requirements, including the documentation of a Company hedging strategy, statistical analysis to qualify a commodity for hedge accounting both on a historical and a prospective basis, and strict contemporaneous documentation that is required at the time each hedge is designated by the Company. This statistical analysis involves utilizing regression analyses that compare changes in the price of jet fuel to changes in the prices of the commodities used for hedging purposes |
| Compensation Related Costs | Grants of RSUs result in the creation of a deferred tax asset, which is a temporary difference, until the time the RSU vests. All excess tax benefits and tax deficiencies are recorded through the income statement. Due to the treatment of RSUs for tax purposes, the Company’s effective tax rate from year to year is subject to variability. |
| Employee Retirement Plans | Unrecognized prior service cost is expensed using a straight-line amortization of the cost over the average future service of Employees expected to receive benefits under the plans. Actuarial gains are amortized utilizing the minimum amortization method. The following actuarial assumptions were used to account for the Company’s postretirement benefit plans at December 31, 2018 , 2017 , and 2016 : 2018 2017 2016 Weighted-average discount rate 4.35 % 3.65 % 4.25 % Assumed healthcare cost trend rate (a) 7.13 % 7.08 % 7.08 % (a) The assumed healthcare cost trend rate is assumed to be 7.13% for 2019 , then decline gradually to 5.19% by 2027 and remain level thereafter. The selection of a discount rate is made annually and is selected by the Company based upon comparison of the expected future cash flows associated with the Company’s future payments under its consolidated postretirement obligations to a yield curve created using high quality bonds that closely match those expected future cash flows. This rate increased during 2018 due to market conditions. The assumed healthcare trend rate is also reviewed at least annually and is determined based upon both historical experience with the Company’s healthcare benefits paid and expectations of how those trends may or may not change in future years. |
