
	Year Ended December 31,
(in millions)	2019		2018		2017
Ticket	$	36,908	$	34,950	$	32,467
Loyalty travel awards	2,900		2,651		2,403
Travel-related services	2,469		2,154		2,077
Total passenger revenue	$	42,277	$	39,755	$	36,947

Passenger Tickets. We defer sales of passenger tickets to be flown by us or that we sell on behalf of other airlines in air traffic liability. Passenger revenue is recognized when we provide transportation or when ticket breakage occurs. For tickets that we sell on behalf of other airlines, we reduce the air traffic liability when consideration is remitted to those airlines. We periodically evaluate the estimated air traffic liability and record any adjustments in our income statement. These adjustments relate primarily to refunds, exchanges, ticket breakage, transactions with other airlines and other items for which final settlement occurs in periods subsequent to the sale of the related tickets at amounts other than the original sales price.

Approximately $3.8 billion, $3.5 billion and $3.5 billion of the prior year air traffic liability related to passenger ticket sales (which excludes those tickets sold on behalf of other airlines) was recognized in passenger revenue during the years ended December 31, 2019, 2018 and 2017, respectively.

Regional Carriers. Our regional carriers include both third-party regional carriers with which we have contract carrier agreements ("contract carriers") and Endeavor Air, Inc., our wholly owned subsidiary. Our contract carrier agreements are primarily structured as capacity purchase agreements where we purchase all or a portion of the contract carrier's capacity and are responsible for selling the seat inventory we purchase. We record revenue related to our capacity purchase agreements in passenger revenue and the related expenses in regional carriers expense, excluding fuel.

Loyalty travel awards revenue is related to the redemption of miles for travel. We recognize loyalty travel awards revenue in passenger revenue as miles are redeemed and transportation is provided. See below for discussion of our loyalty program accounting policies.

Travel-related services are primarily composed of services performed in conjunction with a passenger’s flight, including administrative fees (such as ticket change fees), baggage fees and on-board sales. We recognize revenue for these services when the related transportation service is provided.

Our SkyMiles loyalty program generates customer loyalty by rewarding customers with incentives to travel on Delta. This program allows customers to earn mileage credits ("miles") by flying on Delta, Delta Connection and other airlines that participate in the loyalty program. When traveling, customers earn redeemable miles based on the passenger's loyalty program status and ticket price. Customers can also earn miles through participating companies such as credit card companies, hotels, car rental agencies and ridesharing companies. To facilitate transactions with participating companies, we sell miles to non-airline businesses, customers and other airlines. Miles are redeemable by customers in future periods for air travel on Delta and other participating airlines, membership in our Sky Club and other program awards.

To reflect the miles earned, the loyalty program includes two types of transactions that are considered revenue arrangements with multiple performance obligations: (1) miles earned with travel and (2) miles sold to participating companies.

Passenger Ticket Sales Earning Miles. Passenger ticket sales earning miles under our loyalty program provide customers with (1) miles earned and (2) air transportation, which are considered performance obligations. We value each performance obligation on a standalone basis. To value the miles earned, we consider the quantitative value a passenger receives by redeeming miles for a ticket rather than paying cash, which is referred to as equivalent ticket value ("ETV"). Our estimate of ETV is adjusted for miles that are not likely to be redeemed ("breakage"). We use statistical models to estimate breakage based on historical redemption patterns. A change in assumptions as to the actual redemption activity for miles or the estimated fair value of miles expected to be redeemed could have a material impact on our revenue in the year in which the change occurs and in future years. We recognize breakage proportionally during the period in which the remaining miles are actually redeemed.

We defer revenue for the miles when earned and recognize loyalty travel awards in passenger revenue as the miles are redeemed and transportation is provided. We record the air transportation portion of the passenger ticket sales in air traffic liability and recognize passenger revenue when we provide transportation or if the ticket goes unused.

Sale of Miles. Customers may earn miles based on their spending with participating companies such as credit card companies, hotels, car rental agencies and ridesharing companies with which we have marketing agreements to sell miles. Our contracts to sell miles under these marketing agreements have multiple performance obligations. Payments are typically due monthly based on the volume of miles sold during the period, and the terms of our marketing contracts are from one to eleven years. During the years ended December 31, 2019, 2018 and 2017, total cash sales from marketing agreements were $4.2 billion, $3.5 billion and $3.2 billion, respectively, which are allocated to travel and other performance obligations, as discussed below.

Our most significant contract to sell miles relates to our co-brand credit card relationship with American Express. Our agreements with American Express provide for joint marketing, grant certain benefits to Delta-American Express co-branded credit card holders ("cardholders") and American Express Membership Rewards program participants, and allow American Express to market its services or products using our customer database. Cardholders earn miles for making purchases using co-branded cards, and certain cardholders may also check their first bag for free, are granted discounted access to Delta Sky Club lounges and receive priority boarding and other benefits while traveling on Delta. Additionally, participants in the American Express Membership Rewards program may exchange their points for miles under the loyalty program. We sell miles at agreed-upon rates to American Express which are then provided to their customers under the co-brand credit card program and the Membership Rewards program.

We account for marketing agreements, including those with American Express, by allocating the consideration received to the individual products and services delivered. We allocate the value based on the relative selling prices of those products and services, which generally consist of award travel, priority boarding, baggage fee waivers, lounge access and the use of our brand. We determine our best estimate of the selling prices by using a discounted cash flow analysis using multiple inputs and assumptions, including: (1) the expected number of miles awarded and number of miles redeemed, (2) ETV for the award travel obligation adjusted for breakage, (3) published rates on our website for baggage fees, discounted access to Delta Sky Club lounges and other benefits while traveling on Delta, (4) brand value (using estimated royalties generated from the use of our brand) and (5) volume discounts provided to certain partners.

Effective January 1, 2019, we amended our co-brand agreement with American Express, and we also amended other agreements with American Express during the current year. The new agreements increase the value we receive and extend the terms to 2029. The products and services delivered are consistent with previous agreements, and we continue to allocate the consideration received based on the relative selling prices of those products and services.

We defer the amount for award travel obligation as part of loyalty program deferred revenue and recognize loyalty travel awards in passenger revenue as the miles are used for travel. Revenue allocated to services performed in conjunction with a passenger’s flight, such as baggage fee waivers, is recognized as travel-related services in passenger revenue when the related service is performed. Revenue allocated to access Delta Sky Club lounges is recognized as miscellaneous in other revenue as access is provided. Revenue allocated to the remaining performance obligations, primarily brand value, is recorded as loyalty program in other revenue as miles are delivered.

Current Activity of the Loyalty Program. Miles are combined in one homogeneous pool and are not separately identifiable. As such, the revenue is comprised of miles that were part of the loyalty program deferred revenue balance at the beginning of the period as well as miles that were issued during the period.

The table below presents the activity of the current and noncurrent loyalty program liability, and includes miles earned through travel and miles sold to participating companies, which are primarily through marketing agreements.

Operating revenue for the airline segment is recognized in a specific geographic region based on the origin, flight path and destination of each flight segment. The majority of the revenues of the refinery, consisting of fuel sales to the airline, have been eliminated in the Consolidated Financial Statements. The remaining operating revenue for the refinery segment is included in the domestic region. Our passenger and operating revenue by geographic region is summarized in the following table:


	Passenger Revenue										Operating Revenue
	Year Ended December 31,										Year Ended December 31,
(in millions)	2019		2018		2017		2019		2018		2017
Domestic	$	30,367	$	28,159	$	26,079	$	33,284	$	31,233	$	28,850
Atlantic	6,381		6,165		5,537		7,363		7,042		6,297
Latin America	3,002		2,888		2,862		3,343		3,181		3,133
Pacific	2,527		2,543		2,469		3,017		2,982		2,858
Total	$	42,277	$	39,755	$	36,947	$	47,007	$	44,438	$	41,138


	Year Ended December 31,
(in millions)	2019		2018		2017
Loyalty program	$	1,962	$	1,459	$	1,269
Ancillary businesses and refinery	1,297		1,801		1,591
Miscellaneous	718		558		587
Total other revenue	$	3,977	$	3,818	$	3,447

Loyalty Program. Loyalty program revenues relate primarily to brand usage by third parties and include the redemption of miles for non-travel awards. These revenues are included within the total cash sales from marketing agreements, discussed above.

Ancillary Businesses and Refinery. Ancillary businesses and refinery includes aircraft maintenance provided to third parties, our vacation wholesale operations, our private jet operations and refinery sales to third parties. Third-party refinery production sales are at or near cost; accordingly, the margin on these sales is de minimis. See Note 15, "Segments," for more information on revenue recognition within our refinery segment.

In January 2020, we combined Delta Private Jets, our wholly owned subsidiary which provides private jet operations, with Wheels Up. Upon closing, we received an equity stake in Wheels Up and Delta Private Jets will no longer be reflected in ancillary businesses and refinery. See Note 4, "Investments," for more information on this transaction.

In 2018, we sold DAL Global Services, LLC ("DGS"), which provides aviation-related, ground support equipment maintenance and professional security services, to AirCo Aviation Services, LLC ("AirCo"), a subsidiary of Argenbright Holdings, LLC. Accordingly, DGS is no longer reflected within ancillary businesses and refinery in 2019.

Accounts receivable primarily consist of amounts due from credit card companies from the sale of passenger tickets, ancillary businesses and refinery sales, and other companies for the purchase of miles under the loyalty program. We provide an allowance for uncollectible accounts equal to the estimated losses expected to be incurred based on historical chargebacks, write-offs, bankruptcies and other specific analyses. Bad debt expense was not material in any period presented.