Revenue Recognition We recognize revenue when control of a good or service is transferred to a customer. We consider control to be transferred when the customer has the ability to direct the use of and obtain substantially all of the remaining benefits of that good or service. Significant judgments in the determination of the amount and timing of revenue from contracts with customers include the identification of distinct performance obligations in contracts containing bundled advertising sales and content licenses and the allocation of the consideration among individual performance obligations within these arrangements based on their relative standalone selling prices. Advertising Revenues : Revenue from the sale of advertising earned by the Media Networks segment is recognized when the advertisement is aired. Advertising revenues are principally generated from the sale of advertising campaigns comprised of multiple commercial units. In contracts with guaranteed impressions, we have identified the overall advertising campaign as the performance obligation to be satisfied over time, and impressions delivered against the satisfaction of our guarantee as the measure of progress. To the extent amounts billed exceed the amount of revenue recognized by applying the measure of progress, such amounts are deferred until the impression guarantee has been satisfied. For arrangements that do not include impression guarantees, the individual spots are the performance obligation, and consideration is allocated among the individual advertising spots based on relative standalone selling prices. Affiliate Revenues : In the Media Networks segment, content is primarily distributed through its live network feeds via content license arrangements with affiliate partners, including cable television operators, direct-to-home satellite operators and mobile networks. We also license our content through television, subscription video-on-demand (SVOD) and over-the-top (OTT) distributors, syndication and transactional video-on-demand. As discussed further in the Filmed Entertainment Revenues section below, revenue associated with these arrangements is recognized upon a transfer of control, which occurs upon delivery and availability for use by the licensee. Affiliate revenues from cable television operators, direct-to-home satellite television operators and mobile networks are recognized by the Media Networks segment as the live feeds are provided to the distributor, representing a transfer of control. The performance obligation under such affiliate agreements is a license to our content via the continuous delivery of live linear feeds, and may also include a license to programming for video-on-demand (VOD) viewing. Both performance obligations are satisfied over the term of the agreement. The majority of our affiliate revenues relate to sales-based royalties for which we receive a contractual rate per subscriber. Revenue for these contracts is recognized when the sale to the end customer occurs, which is generally concurrent with the delivery of the linear feeds based on the number of subscribers the customer has at the time of delivery. Consumer Products, Recreation and Live Events Revenues : Revenue associated with consumer products, recreation and live event contracts is typically recognized utilizing contractual royalty rates applied to sales amounts reported by licensees. When consumer products and recreation agreements include minimum guaranteed consideration, revenue is recognized as sales occur by the licensee or ratably if the sales-based consideration is not expected to exceed a minimum guaranteed amount of consideration. For live events, we recognize revenue when the event is held. Filmed Entertainment Revenues : In the Filmed Entertainment segment, we license our content through theatrical releases, television, SVOD and OTT distributors, and through transactional video-on-demand. We also distribute our films through DVD and Blu-ray sales through wholesale and retail partners. Revenue from the licensing of film and television exhibition rights, including broadcast and cable television networks, SVOD and other OTT services, is recognized upon a transfer of control, which occurs upon delivery and availability for use by the licensee. Each individual title delivered represents a separate performance obligation. For renewals or extensions of licensing arrangements, revenue related to the renewal or extension is recognized upon the start of the renewal or extension period to the extent the content has been delivered to the customer. SVOD and other OTT arrangements include content made available to distributors on one or more dates for a fixed fee. Consideration for such arrangements is allocated among the titles and episodes based on relative standalone selling prices. Estimation of standalone selling prices requires judgment, which can impact the timing and amount of revenue that we recognize. In determining the transaction price of a contract, an adjustment is made if payment from our customer occurs either significantly before or after performance, resulting in a significant financing component. Applying a practical expedient in the new standard, we do not assess whether a significant financing component exists if the period between when we perform our obligations under the contract and when the customer pays is one year or less. In transactional video-on-demand and similar arrangements, our performance obligation is to provide the content to our distribution customers that provide our content to end users. These contracts provide for sales-based royalties based on the number of underlying transactions with end users. Revenue for transactional video-on-demand and similar arrangements is recognized as the content is exhibited based on end-customer purchases as reported by distributors. Similarly, revenue from licensing of our content through electronic sell-through means is recognized as each title is downloaded by the end customer, as the customer is able to use the license immediately upon download. For sales of DVDs and Blu-ray discs to wholesalers and retailers, revenue is recognized upon the later of physical delivery to the customer or the date that restrictions on sales by the retailers are lifted. Theatrical revenue is recognized from theatrical distribution of films during the exhibition period. These agreements take the form of sales-based royalties and revenue is recognized when the sale to the end customer occurs. Revenue Allowances : We record a provision for sales returns and allowances at the time of sale based upon an estimate of future returns, rebates and other incentives (estimated returns). In determining estimated returns, we consider numerous sources of qualitative and quantitative evidence including forecasted sales data, customers rights of return, units shipped and units remaining at retail, historical return rates for similar product, current economic trends, competitive environment, promotions and sales strategies. Reserves for sales returns and allowances are recorded as a liability in the Consolidated Balance Sheet. Our reserve for sales returns and allowances was $56 million and $64 million at September 30, 2019 and 2018 , respectively. Subsequent to the adoption of ASC 606, the reserve for sales returns and allowances is presented in Other Liabilities - current , and prior to the adoption it was presented as a reduction to Receivables, net. Reserves for accounts receivable are based on amounts estimated to be uncollectible and are recorded as a contra-receivable. Our allowance for doubtful accounts was $47 million and $45 million at September 30, 2019 and 2018 , respectively. Gross versus Net Revenue : We earn and recognize revenues under certain third-party distribution and outsourced advertising sales agreements. In such cases, determining whether revenue should be reported on a gross or net basis is based on managements assessment of which party controls the good or service being transferred to the customer.