assets for impairment, the actual amounts may differ materially from these estimates. In addition, we consider the amount the intangible assets' fair value exceeded their carrying value in the most recent fair value measurement using a quantitative approach.  

 

Changes in certain events and circumstances could result in impairment. Factors which could cause impairment include, but are not limited to, (1) negative trends in our market capitalization, (2) an increase in fuel prices, (3) declining passenger mile yields, (4) lower passenger demand as a result of a weakened U.S. and global economy, (5) interruption to our operations due to a prolonged employee strike, terrorist attack, or other reasons and (6) changes to the regulatory environment.  

 

We assessed each of the above assumptions in our most recent impairment analyses. The combination of our most recently completed annual results and our projected revenues, expenses and cash flows more than offset the impact of fuel prices and other airline input costs. The stabilizing operating environment for U.S. airlines has resulted in annual yields increasing along with load factors, leading to improved financial results.  

 

Goodwill. Our goodwill balance was $9.8 billion at December 31, 2013 . We determined that there was no indication that Goodwill was impaired based upon our qualitative assessment of all relevant factors, including applicable factors noted in " Key Assumptions " above.  

 

Identifiable Intangible Assets. Our identifiable intangible assets had a net carrying amount of $4.7 billion at December 31, 2013 . Indefinitelived assets are not amortized and consist primarily of routes, slots, the Delta tradename and assets related to SkyTeam and collaborative arrangements.  

 

In 2013, we determined that there was no indication that our indefinite-lived intangible assets were impaired based upon our assessments. These assessments included analyses and weighting of all relevant factors, including the significant inputs and key assumptions which impact the fair value of our indefinite-lived intangible assets.  

 

Long-Lived Assets  

 

Our flight equipment and other long-lived assets have a recorded value of $21.9 billion at December 31, 2013 . This value is based on various factors, including the assets' estimated useful lives and salvage values. We record impairment losses on flight equipment and other long-lived assets used in operations when events and circumstances indicate the assets may be impaired and the estimated future cash flows generated by those assets are less than their carrying amounts. Factors which could cause impairment include, but are not limited to, (1) a decision to permanently remove flight equipment or other long-lived assets from operations, (2) significant changes in the estimated useful life, (3) significant changes in projected cash flows, (4) permanent and significant declines in fleet fair values and (5) changes to the regulatory environment. For long-lived assets held for sale, we discontinue depreciation and record impairment losses when the carrying amount of these assets is greater than the fair value less the cost to sell.  

 

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