2013 that allocates the consideration received to the individual products and services delivered based on their relative selling prices. The increased value received under the amended agreements will increase the amount of deferred revenue for the travel component and increase the value of the other deliverables, which are recognized in other revenue as they are provided.  

 

In September 2013, we modified our marketing agreements with American Express that required us to change the accounting method for recording SkyMiles sold. Under the previous method, the embedded premium or discount was allocated to the residual products or services in a combined transaction. The new method allocates consideration received based on the relative selling price of each product or service. We determined our best estimate of the selling prices by considering discounted cash flow analysis using multiple inputs and assumptions, including: (1) the expected number of miles awarded and number of miles redeemed, (2) the rate at which we sell mileage credits to other airlines, (3) published rates on our website for baggage fees, access to Delta Sky Club lounges and other benefits while traveling on Delta and (4) brand value. The impact of adopting the relative selling price method re-allocated a portion of the embedded discount to the travel component, lowering the deferral rate we use to record miles sold under the agreements and increasing revenue recognized on the remaining deliverables.  

 

We recognize revenue as we deliver each sales element. We defer the travel deliverable (miles) as part of frequent flyer deferred revenue and recognize passenger revenue as the mileage credits are used for travel. The revenue allocated to the remaining deliverables is recorded in other revenue. We recognize the revenue for these services as they are performed.  

 

Breakage. For mileage credits that we estimate are not likely to be redeemed (“breakage”), we recognize the associated value proportionally during the period in which the remaining mileage credits are expected to be redeemed. Management uses statistical models to estimate breakage based on historical redemption patterns. A change in assumptions as to the period over which mileage credits are expected to be redeemed, the actual redemption activity for mileage credits or the estimated fair value of mileage credits expected to be redeemed could have a material impact on our revenue in the year in which the change occurs and in future years. At December 31, 2014 , the aggregate deferred revenue balance associated with the SkyMiles Program was $4.2 billion . A hypothetical 1% change in the number of outstanding miles estimated to be redeemed would result in a $28 million impact on our deferred revenue liability at December 31, 2014 .  

 

Goodwill and Indefinite-Lived Intangible Assets  

 

We apply a fair value-based impairment test to the carrying value of goodwill and indefinite-lived intangible assets on an annual basis (as of October 1) and, if certain events or circumstances indicate that an impairment loss may have been incurred, on an interim basis. We assess the value of our goodwill and