GOODWILL AND OTHER INTANGIBLE ASSETS

Changes in the carrying amount of goodwill follow:



(Dollars in millions)	Additives & Functional Products			Advanced Materials			Chemical Intermediates			Other		Total
Balance at December 31, 2016	$	2,416		$	1,275		$	760		$	10	$	4,461
Acquisitions	17			—			—			—		17
Goodwill written off as a result of sale of business	(1		)	—			—			—		(1		)
Currency translation adjustments	27			14			9			—		50
Balance at December 31, 2017	2,459			1,289			769			10		4,527
Impairments recognized	(38		)	—			—			—		(38		)
Currency translation adjustments	(11		)	(6		)	(5		)	—		(22		)
Balance at December 31, 2018	$	2,410		$	1,283		$	764		$	10	$	4,467

In fourth quarter 2018, as a result of the annual impairment test of goodwill, the Company recognized a $38 million goodwill impairment in the crop protection reporting unit (part of the Additives & Functions Products ("AFP") segment). The impairment was primarily driven by an increase in the WACC applied to the impairment analysis and the estimated impact of future regulatory changes. The Company used an income approach and applied a fair value methodology based on discounted cash flows in testing the carrying value of goodwill for the crop protection reporting unit.

As of December 31, 2018, the reported balance of goodwill included accumulated impairment losses of $61 million, $12 million, and $14 million in the AFP segment, Chemical Intermediates ("CI") segment, and other segments, respectively. As of December 31, 2017, the reported balance of goodwill included accumulated impairment losses of $23 million, $12 million, and $14 million in the AFP segment, CI segment, and other segments, respectively.

The carrying amounts of intangible assets follow:



				December 31, 2018						December 31, 2017
(Dollars in millions)	Estimated Useful Life in Years			Gross Carrying Value		Accumulated Amortization		Net Carrying Value		Gross Carrying Value		Accumulated Amortization		Net Carrying Value
Amortizable intangible assets:
Customer relationships	8	-	25	$	1,567	$	419	$	1,148	$	1,583	$	345	$	1,238
Technology	7	-	20	680		294		386		690		247		443
Contracts		5		180		147		33		180		111		69
Other	5	-	37	102		23		79		102		19		83

Indefinite-lived intangible assets:
Tradenames				529		—		529		530		—		530
Other				10		—		10		10		—		10
Total identified intangible assets				$	3,068	$	883	$	2,185	$	3,095	$	722	$	2,373

Amortization expense of definite-lived intangible assets was $164 million, $164 million, and $166 million for 2018, 2017, and 2016, respectively. Estimated amortization expense for future periods is $165 million in 2019, $130 million in 2020, and $120 million each year for 2021 through 2023.