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 Companys 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 Companys 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 Companys 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 Companys 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 obligations 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 Companys 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 Companys 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 .