we will record an impairment charge for the difference in fair value and carrying value.

When we evaluate goodwill for impairment using a quantitative approach, we estimate the fair value of the reporting unit by considering both market capitalization and projected discounted future cash flows (an income approach). When we perform a quantitative impairment assessment of our indefinite-lived intangible assets, fair value is estimated based on (1) recent market transactions, where available, (2) the royalty method for the Delta tradename (which assumes hypothetical royalties generated from using our tradename) or (3) projected discounted future cash flows (an income approach).

Key Assumptions. The key assumptions in our impairment tests include: (1) forecasted revenues, expenses and cash flows, (2) terminal period revenue growth and cash flows, (3) an estimated weighted average cost of capital, (4) assumed discount rates depending on the asset and (5) a tax rate. These assumptions are consistent with those hypothetical market participants would use. Since we are required to make estimates and assumptions when evaluating goodwill and indefinite-lived intangible assets for impairment, actual transaction amounts may differ materially from these estimates. In addition, we consider the amount by which the intangible assets' fair values exceeded their respective carrying values in the most recent fair value measurements calculated 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) reduced profitability resulting from lower passenger mile yields or higher input costs (primarily related to fuel and employees), (3) lower passenger demand as a result of weakened U.S. and global economies, (4) interruption to our operations due to a prolonged employee strike, terrorist attack, or other reasons, (5) changes to the regulatory environment (e.g., diminished slot restrictions or additional Open Skies agreements), (6) competitive changes by other airlines and (7) strategic changes to our operations leading to diminished utilization of the intangible assets.

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 any negative events and circumstances. 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, which is related to the airline segment, was $9.8 billion at December 31, 2015 . Based upon our quantitative assessment of all relevant factors, including applicable factors noted in " Key Assumptions " above, we determined that the fair value of goodwill significantly exceeded the carrying value and, therefore, there was no indication that goodwill was impaired.

Identifiable Intangible Assets. Our identifiable intangible assets, which are related to the airline segment, had a net carrying