(6)  Goodwill and Other Intangible Assets

Goodwill and Indefinite Lived Intangible Assets

Changes in the carrying amount of goodwill are as follows (amounts in millions):

As presented in the accompanying consolidated balance sheets, trademarks are the other significant indefinite lived intangible asset. See the disclosure below for information related to the 2017 impairment of the Company’s trademarks. Other fluctuations in the trademark balance from the prior year were due to the change in foreign exchange rates.

Intangible Assets subject to amortization

Intangible assets subject to amortization are comprised of the following:

Intangible assets are being amortized on an accelerated basis as reflected in amortization expense and in the future amortization table below.

Amortization expense was $137 million, $188 million and $198 million for the years ended December 31, 2018,  2017 and 2016, respectively.

The estimated future amortization expense for the next five years related to intangible assets with definite lives as of December 31, 2018, assuming no subsequent impairment of the underlying assets, is as follows (amounts in millions):

Impairments

Due to certain marketplace factors impacting TripAdvisor’s operating results, which led to a decline in TripAdvisor’s stock price, impairment losses of $527 million and $1,271 million were recorded during the year ended December 31, 2017 related to trademarks and goodwill, respectively, related to the hotel reporting unit. The fair value of the trademarks was determined using the relief from royalty method. The fair values of the reporting units were determined using a combination of market multiples (market approach) and discounted cash flow (income approach) calculations (Level 3). As of December 31, 2018, accumulated goodwill impairment losses for TripAdvisor totaled $1,271 million.