NOTE 6 — Goodwill and Intangible Assets, Net

The following table presents our goodwill and intangible assets as of December 31, 2018 and 2017:



	December 31,
	2018		2017
	(In millions)
Goodwill	$	8,120	$	8,229
Intangible assets with indefinite lives	1,400		1,479
Intangible assets with definite lives, net	592		830
	$	10,112	$	10,538

Impairment Assessments. We perform our annual assessment of possible impairment of goodwill and indefinite-lived intangible assets as of October 1, or more frequently if events and circumstances indicate that impairment may have occurred. As of October 1, 2018, we incurred impairment charges related to intangible assets with indefinite-lives of $42 million and goodwill of $25 million both within our Core OTA segment. In addition, during the second quarter of 2018, we incurred goodwill impairment charge of $61 million within our Core OTA segment. In 2017, we had no impairments of goodwill or intangible assets with indefinite-lives.

Goodwill. The following table presents the changes in goodwill by reportable segment:



	Core OTA			trivago			HomeAway			Egencia			Total
	(In millions)
Balance as of January 1, 2017	$	4,703		$	516		$	2,591		$	132		$	7,942
Additions	124			—			—			—			124
Foreign exchange translation and other	13			72			65			13			163
Balance as of December 31, 2017	4,840			588			2,656			145			8,229
Additions	—			—			31			—			31
Impairment charge	(86		)	—			—			—			(86		)
Foreign exchange translation and other	(13		)	(27		)	(5		)	(9		)	(54		)
Balance as of December 31, 2018	$	4,741		$	561		$	2,682		$	136		$	8,120

Any immaterial change in goodwill amounts resulting from purchase accounting adjustments are presented as "Foreign exchange translation and other" in the above table. In 2018 and 2017, the additions to goodwill relate to our acquisitions as described in NOTE 3 — Acquisitions and Other Investments.

As of December 31, 2018 and 2017, accumulated goodwill impairment losses in total were $2.6 billion and $2.5 billion, which was associated with our Core OTA segment.

Indefinite-lived Intangible Assets. Our indefinite-lived intangible assets relate principally to trade names and trademarks acquired in various acquisitions.

Intangible Assets with Definite Lives. The following table presents the components of our intangible assets with definite lives as of December 31, 2018 and 2017:



	December 31, 2018							December 31, 2017
	Cost		Accumulated Amortization			Net		Cost		Accumulated Amortization			Net
	(In millions)
Customer relationships	$	659	$	(419	)	$	240	$	665	$	(304	)	$	361
Supplier relationships	650		(426		)	224		655		(368		)	287
Technology	544		(510		)	34		532		(441		)	91
Domain names	159		(83		)	76		132		(70		)	62
Other	450		(432		)	18		452		(423		)	29
Total	$	2,462	$	(1,870	)	$	592	$	2,436	$	(1,606	)	$	830

Amortization expense was $283 million, $275 million and $317 million for the years ended December 31, 2018, 2017 and 2016. The estimated future amortization expense related to intangible assets with definite lives as of December 31, 2018, assuming no subsequent impairment of the underlying assets, is as follows, in millions:



2019	$	185
2020	143
2021	97
2022	73
2023	39
2024 and thereafter	55
Total	$	592