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Summary of Significant Accounting Policies (Policies) | 12 Months Ended
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Dec. 31, 2019
Accounting Policies [Abstract] |
New Accounting Pronouncements, Policy | On February 25, 2016, the FASB issued the New Lease Standard. 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, as defined in the New Lease Standard) at the lease commencement date and recognize expenses on the income statement in a similar manner to the legacy guidance in ASC 840, Leases ("ASC 840"). The Company adopted the provisions of the New Lease Standard effective January 1, 2019, using 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 elected 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) not reassessing lease classification, and (iii) not revaluing initial direct costs for existing leases. In addition, the New Lease Standard eliminated the previous build-to-suit lease accounting guidance and resulted 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. However, given the Company's guarantee associated with the bonds issued to fund the Dallas Love Field Modernization Program (the "LFMP"), the remaining debt service amount as of the adoption date was considered a minimum rental payment under the New Lease Standard, and therefore was recorded as a lease liability with a corresponding right-of-use asset on the Consolidated Balance Sheet that will be reduced through debt service payments made in 2019 and beyond. See Note 7 for disclosures related to the New Lease Standard, and Note 4 for further information on the Company’s build-to-suit projects. The following table provides the Consolidated Balance Sheet impact of applying the New Lease Standard effective as of January 1, 2019. The impact to the Company's results of operations and cash flows was not significant:
| Balance as of January 1, 2019
(in millions) | Balances removed under prior accounting |  | Balances added under New Lease Standard |  | Net impact of New Lease Standard
Prepaid expenses and other current assets | $ | 1 |  |  | $ | — |  |  | $ | (1 | )
Flight equipment | — |  |  | (110 | ) |  | (110 | )
Assets constructed for others | 1,669 |  |  | — |  |  | (1,669 | )
Less allowance for depreciation and amortization | (166 | ) |  | (2 | ) |  | 164 |
Operating lease right-of-use assets | — |  |  | 1,466 |  |  | 1,466 |
Other assets | 121 |  |  | — |  |  | (121 | )
Total assets | $ | 1,625 |  |  | $ | 1,354 |  |  | $ | (271 | )
Accounts payable | $ | 8 |  |  | $ | — |  |  | $ | (8 | )
Accrued liabilities | 37 |  |  | — |  |  | (37 | )
Current operating lease liabilities | — |  |  | 355 |  |  | 355 |
Current maturities of long-term debt | — |  |  | (14 | ) |  | (14 | )
Long-term debt less current maturities | — |  |  | (96 | ) |  | (96 | )
Deferred income taxes | (17 | ) |  | — |  |  | 17 |
Construction obligation | 1,602 |  |  | — |  |  | (1,602 | )
Noncurrent operating lease liabilities | — |  |  | 1,119 |  |  | 1,119 |
Other noncurrent liabilities | 60 |  |  | — |  |  | (60 | )
Retained earnings | (65 | ) |  | (10 | ) |  | 55 |
Total liabilities and stockholders' equity | $ | 1,625 |  |  | $ | 1,354 |  |  | $ | (271 | )
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, 2019, the Company adopted Accounting Standards Update ("ASU") No. 2016-02, Leases, codified in Accounting Standards Codification ("ASC") 842 (the "New Lease Standard"). All amounts and disclosures set forth in this Form 10-K for the year ended December 31, 2019, reflect the adoption of this ASU, while all periods prior to 2019 remain in accordance with prior accounting requirements. See Note 2 for further information. Effective as of January 1, 2018, the Company adopted 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 this ASU. See Note 2 for further information.
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, 2019, $25 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. As of December 31, 2018, no cash collateral deposits were held by or provided 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 the Company's business partners and other suppliers, credit card companies associated with sales of tickets for future travel, and amounts due from business partners in the Company’s loyalty program. See Note 15 for further information. The allowance for doubtful accounts was immaterial at December 31, 2019 and 2018. In addition, the provision for doubtful accounts and write-offs for 2019, 2018, and 2017 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 immaterial at December 31, 2019, and 2018. In addition, the Company’s provision for obsolescence and write-offs for 2019, 2018, and 2017 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, and 5 to 30 years for ground property and equipment. Residual values estimated for aircraft are approximately 15 percent, and generally range from 0 to 10 percent for ground property and equipment. Assets constructed for others consists of airport improvement projects in which the Company is considered to have control of the asset during the construction period. Once construction is effectively completed, the sale-leaseback model would apply when control passes from the lessee to the lessor. See Note 4 for further information. In September 2017, the Company retired its remaining 61 Boeing 737-300 ("Classic") aircraft as part of an accelerated retirement schedule. This resulted in a change in anticipated retirement dates, which 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 leased aircraft fleet. The impact on expense and earnings from the accelerated depreciation were as follows:
(in millions, except per share amounts) | Year ended December 31, 2017
Depreciation and amortization expense | $ | 21 |
Net income * | $ | (19 | )
Net income per basic share | $ | (0.03 | )
Net income per diluted share | $ | (0.03 | )
* 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.
Leases | Leases The Company determines if an arrangement is a lease at inception. Operating leases are included in Operating lease right-of-use assets, Current operating lease liabilities, and Noncurrent operating lease liabilities in the Consolidated Balance Sheet. Finance leases are included in Property and equipment, Current maturities of long-term debt, and Long-term debt less current maturities in the Consolidated Balance Sheet. Right-of-use assets represent the Company's right to use an underlying asset for the lease term, and lease liabilities represent the Company's obligation to make lease payments arising from the lease. The lease liability is measured as the present value of the unpaid lease payments, and the right-of-use asset value is derived from the calculation of the lease liability. Lease payments 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 do not include (i) variable lease payments other than those that depend on an index or rate, (ii) any guarantee by the lessee of the lessor’s debt, or (iii) any amount allocated to non-lease components, if such election is made upon adoption, per the provisions of the New Lease Standard. The Company uses its estimated incremental borrowing rate, which is derived from information available at the lease commencement date, in determining the present value of lease payments, since the Company does not know the actual implicit rates in its leases. The Company gives consideration to its recent debt issuances as well as publicly available data for instruments with similar characteristics when calculating its incremental borrowing rate. Lease expense for operating lease payments is recognized on a straight-line basis over the lease term. The Company combines lease and nonlease components for all asset groups. The Company's lease term includes any option to extend the lease when it is reasonably certain to be exercised based on considering all relevant economic factors. The Company enters into leases for aircraft, property, and other types of equipment in the normal course of business. The accounting for these leases follows the requirements of the New Lease Standard, which the Company adopted as of January 1, 2019. See Note 2 for further information.
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 agreements that effectively transfer the risk of performance of such work to the service provider. Under the agreements where the risk of performance is deemed transferred to the counterparty, the appropriate expense is recorded commensurate with the period in which the corresponding level of service is provided. Generally, 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. 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, 2019 and 2018:
|  |  | Year ended December 31, 2019 |  | Year ended December 31, 2018
(in millions) | Weighted-average useful life (in years) |  | Gross carrying amount |  | Accumulated amortization |  | Gross carrying amount |  | Accumulated Amortization
Customer relationships/marketing agreements | 12 |  |  | $ | 14 |  |  | $ | 13 |  |  | $ | 27 |  |  | $ | 25 |
Owned domestic slots (a) | Indefinite |  |  | 295 |  |  | n/a |  |  | 295 |  |  | n/a |
Gate leasehold rights (b) | — |  |  | — |  |  | — |  |  | 180 |  |  | 78 |
Total | 12 |  |  | $ | 309 |  |  | $ | 13 |  |  | $ | 502 |  |  | $ | 103 |
(a) Intangible assets primarily consist of acquired rights to certain airport owned takeoff and landing slots (a "slot" is the right of an air carrier, pursuant to regulations of the Federal Aviation Administration ("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. (b) Airport gate leasehold rights are classified as right-of-use assets upon adoption of the New Lease Standard. See Note 7. The Company's definite lived intangible assets are amortized on a straight-line basis over the useful life of the asset. The aggregate amortization expense for 2019, 2018, and 2017 was $15 million, $16 million, and $13 million, respectively. Estimated aggregate amortization expense for the five succeeding years and thereafter is immaterial
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, funds that are past flight date and remain unused, but are expected to be used in the future, and the Company’s liability for loyalty benefits that are expected to be redeemed in the future. The majority of the Company’s tickets sold are nonrefundable. Southwest has a No Show policy that applies to fares that are not canceled or changed by a Customer at least ten minutes prior to a flight's scheduled departure. Nonrefundable tickets that are sold but not flown on the travel date, and are canceled in accordance with the No Show policy, can be applied to future travel. Refundable tickets that are sold but not flown on the travel date can also be applied to future travel. A small percentage of tickets (or partial tickets) expire unused. The Company estimates the amount of tickets that expire unused and recognizes such amounts in Passenger revenue once the scheduled flight date has lapsed in proportion to the pattern of flights taken by the Customer. 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 services are also recognized when the service is provided, which is typically the flight date. Initial spoilage estimates for both tickets and funds available for future use are routinely adjusted and ultimately finalized once the tickets expire, which is typically twelve months after the original purchase date. 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. See Note 5 for further information. Approximately $615 million, approximately $566 million, and approximately $489 million of the Company's Operating revenues in 2019, 2018, and 2017, respectively, were attributable to foreign operations. The remainder of the Company's Operating revenues, approximately $21.8 billion, approximately $21.4 billion, and approximately $20.7 billion in 2019, 2018, and 2017, 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 and 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 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 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 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) 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 remain 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. Due to the size of the Company’s liability for loyalty benefits, changes in Customer behavior and/or expected future redemption patterns could result in significant variations in Passenger revenue.
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. 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 marketing 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 remain 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. The Company’s liability for loyalty benefits includes a portion that is expected to be redeemed during the following twelve months (classified as a component of Air traffic liability), and a portion that is not expected to be redeemed during the following twelve months (classified as Air traffic liability - noncurrent). The Company continually updates this analysis and adjusts the split between current and non-current liabilities as appropriate. 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, 2019, 2018, and 2017 was $212 million, $215 million, and $224 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. 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.Outstanding RSUs vest over three years, subject generally to the individual’s continued employment or service. The PBRSUs granted in 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 are also subject generally to the individual’s continued employment or service. The PBRSUs granted in January 2018 and January 2019 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 are also subject generally to 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.
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 Company has forward-starting interest rate swap agreements, the primary objective of which is to hedge forecasted debt issuances and aircraft leases. 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. 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, 2019, 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. 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.
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 $630 million and $674 million at December 31, 2019, and 2018, respectively. Computer software depreciation expense was $177 million, $155 million, and $168 million for the years ended December 31, 2019, 2018, and 2017, 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 2019, 2018, or 2017.
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. See Note 14 for further information.
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, Dispatchers, Flight Crew Training Instructors, and Meteorologists, which had contracts that became amendable on or before December 31, 2019, are in discussions on labor agreements. Those unionized Employee groups in discussions represent approximately 40 percent of the Company’s full-time equivalent Employees as of December 31, 2019. 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, 2019, the Company operated an all-Boeing fleet, all of which are variations of the Boeing 737. The Boeing 737 MAX aircraft ("MAX") are crucial to the Company’s growth plans and fleet modernization initiatives. On March 13, 2019, the FAA issued an emergency order for all U.S. airlines to ground the MAX aircraft, including the 34 MAX aircraft in the Company’s fleet. The MAX aircraft remains grounded and, based on continued uncertainty around the timing of the MAX return to service, the Company has removed the MAX from its flight schedule through June 6, 2020. Based on recent guidance from Boeing estimating that the ungrounding of the MAX will be mid-2020, the Company will likely extend MAX-related flight schedule adjustments further to provide operational reliability and dependable flight schedules for our Customers booking their summer travel. Further, MAX deliveries have remained suspended following the MAX groundings and Boeing is not currently manufacturing new MAX aircraft. The Company does not know whether, on what conditions, or when the MAX groundings will end. Regulatory approval of MAX return to service is subject to Boeing's ongoing work with the FAA, who will determine the timing of MAX return to service. The MAX groundings adversely affected operating results for the year ended December 31, 2019, and could have a material, adverse effect on the Company's operating results in future periods. A continued prolonged extension or permanent grounding of the MAX aircraft would require additional flight schedule adjustments and result in further delays in aircraft deliveries, as well as lower operating revenues, operating income, and net income due to a variety of factors, including, among others, (i) lost revenue due to flight cancellations and disruptions as a result of a smaller operating aircraft fleet, (ii) the lack of ability to make corresponding reductions in expenses because of the fixed nature of many expenses, and (iii) possible negative effects on Customer confidence and airline choice. Boeing no longer manufactures versions of the 737 other than the 737 MAX family of aircraft. If the 737 MAX aircraft were to remain unavailable for the Company’s flight operations, the Company’s growth would be restricted unless and until it could procure and operate other types of aircraft from Boeing or another manufacturer, seller, or lessor, and the Company’s operations would be materially adversely affected. In particular, if the Company’s growth were to be dependent upon the introduction of a new aircraft make and model to the Company’s fleet, the Company would need to, among other things, (i) develop and implement new maintenance, operating, and training programs, (ii) secure extensive regulatory approvals, and (iii) implement new technologies. The requirements associated with operating a new aircraft make and model could take an extended period of time to fulfill and would likely impose substantial costs on the Company. A shift away from a single fleet type could also add complexity to the Company’s operations, present operational and compliance risks, and materially increase the Company's costs. Any of these events would have a material, adverse effect on the Company's business, operating results, and financial condition. The Company could also be materially adversely affected if the pricing or operational attributes of its aircraft were to become less competitive. See Note 16 for further information. 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 ten 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 | 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" or "critical terms match" methods of accounting, ineffectiveness is assessed at each reporting period. If hedge accounting is achieved, all periodic changes in fair value of the interest rate swaps are recorded in AOCI. 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. 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. 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 2019, 2018, or 2017. 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 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. 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. No cash collateral deposits were provided by or held by the Company based on its outstanding interest rate swap agreements.
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, 2019, 2018, and 2017:
|  | 2019 |  | 2018 |  | 2017
Weighted-average discount rate |  | 3.30 | % |  | 4.35 | % |  | 3.65 | %
Assumed healthcare cost trend rate (a) |  | 7.13 | % |  | 7.13 | % |  | 7.08 | %
(a) | The assumed healthcare cost trend rate is expected to be 6.79% for 2020, 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 decreased during 2019 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.

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- Definition Disclosure of accounting policy for long-lived, physical assets used in the normal conduct of business and not intended for resale. Includes, but is not limited to, basis of assets, depreciation and depletion methods used, including composite deprecation, estimated useful lives, capitalization policy, accounting treatment for costs incurred for repairs and maintenance, capitalized interest and the method it is calculated, disposals and impairments. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02.13(a)) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 360 -SubTopic 10 -Section 50 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=6391035&loc=d3e2868-110229 Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 235 -SubTopic 10 -Section 50 -Paragraph 3 -URI http://asc.fasb.org/extlink&oid=84158767&loc=d3e18780-107790 + Details
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- Definition Disclosure of accounting policy for receivable. Includes, but is not limited to, accounts receivable and financing receivable. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 235 -SubTopic 10 -Section 50 -Paragraph 3 -URI http://asc.fasb.org/extlink&oid=84158767&loc=d3e18780-107790 Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef -Publisher FASB -Name Accounting Standards Codification -Topic 310 -SubTopic 10 -Section 50 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=118936363&loc=d3e5033-111524 Reference 3: http://www.xbrl.org/2009/role/commonPracticeRef -Publisher FASB -Name Accounting Standards Codification -Topic 310 -SubTopic 20 -Section 50 -Paragraph 4 -URI http://asc.fasb.org/extlink&oid=84159169&loc=d3e10178-111534 Reference 4: http://www.xbrl.org/2009/role/commonPracticeRef -Publisher FASB -Name Accounting Standards Codification -Topic 310 -SubTopic 20 -Section 50 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=84159169&loc=d3e10149-111534 Reference 5: http://www.xbrl.org/2009/role/commonPracticeRef -Publisher FASB -Name Accounting Standards Codification -Topic 310 -SubTopic 20 -Section 50 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=84159169&loc=d3e10133-111534 + Details
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- Definition Disclosure of accounting policy for revenue. Includes revenue from contract with customer and from other sources. + References Reference 1: http://www.xbrl.org/2003/role/exampleRef -Publisher FASB -Name Accounting Standards Codification -Topic 235 -SubTopic 10 -Section 50 -Paragraph 4 -Subparagraph (e) -URI http://asc.fasb.org/extlink&oid=84158767&loc=d3e18823-107790 Reference 2: http://www.xbrl.org/2003/role/exampleRef -Publisher FASB -Name Accounting Standards Codification -Topic 235 -SubTopic 10 -Section 50 -Paragraph 4 -Subparagraph (f) -URI http://asc.fasb.org/extlink&oid=84158767&loc=d3e18823-107790 + Details
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- Definition Disclosure of accounting policy for award under share-based payment arrangement. Includes, but is not limited to, methodology and assumption used in measuring cost. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 235 -SubTopic 10 -Section 50 -Paragraph 3 -URI http://asc.fasb.org/extlink&oid=84158767&loc=d3e18780-107790 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (b),(f) -URI http://asc.fasb.org/extlink&oid=116856206&loc=d3e5070-113901 Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=116856206&loc=d3e5047-113901 + Details
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