The following is a progression of goodwill by reportable segment for the years ended September 30, 2019 and 2018.

	Specialty			Intermediates
(In millions)	Ingredients			and Solvents (a)		Total
Balance at September 30, 2017	$	2,315		$	—	$	2,315
Acquisition (b)		5			—		5
Currency translation		(16	)		—		(16	)
Balance at September 30, 2018		2,304			—		2,304
Currency translation		(51	)		—		(51	)
Balance at September 30, 2019	$	2,253		$	—	$	2,253

Other intangible assets were comprised of the following as of September 30, 2019 and 2018.

	2019							2018
	Gross					Net		Gross					Net
	carrying		Accumulated			carrying		carrying		Accumulated			carrying
(In millions)	amount		amortization			amount		amount		amortization			amount
Definite-lived intangible assets
Trademarks and trade names	$	66	$	(29	)	$	37	$	66	$	(25	)	$	41
Intellectual property		712		(391	)		321		721		(350	)		371
Customer and supplier relationships		744		(292	)		452		759		(264	)		495
Total definite-lived intangible assets		1,522		(712	)		810		1,546		(639	)		907

Indefinite-lived intangible assets
Trademarks and trade names		278		—			278		278		—			278
Total intangible assets	$	1,800	$	(712	)	$	1,088	$	1,824	$	(639	)	$	1,185

Intangible assets classified as definite-lived are amortized on a straight-line basis over their estimated useful lives. Useful lives range from 3 to 25 years for trademarks and trade names; 5 to 25 years for intellectual property; and 3 to 24 years for customer and supplier relationships.

Amortization expense recognized on intangible assets was $86 million for 2019, $93 million for 2018 and $80 million for 2017, and is primarily included in the selling, general and administrative expense caption of the Statements of Consolidated Comprehensive Income. As of September 30, 2019, all of Ashland’s intangible assets that had a carrying value were being amortized except for certain trademarks and trade names that have been determined to have indefinite lives. Estimated amortization expense for future periods is $86 million in 2020, $85 million in 2021, $85 million in 2022, $85 million in 2023 and $71 million in 2024. The amortization expense for future periods is an estimate. Actual amounts may change from such estimated amounts due to fluctuations in foreign currency exchange rates, additional intangible asset acquisitions and divestitures, potential impairment, accelerated amortization, or other events.

Ashland reviews goodwill for impairment annually or when events and circumstances indicate an impairment may have occurred. This annual assessment is performed as of July 1 and consists of Ashland determining each reporting unit’s current fair value compared to its current carrying value. Ashland tests goodwill either quantitatively or qualitatively for impairment.

For the qualitative approach, Ashland considers relevant events and circumstances such as macroeconomic conditions, industry and market considerations, overall financial performance and changes in management and business strategy, changes in carrying value, among others. Ashland considers how these relevant events and circumstances change between quantitative goodwill impairment tests. Ashland decides whether it is more likely than not that the fair value of its reporting units exceeds the carrying values. If not, a quantitative assessment must be performed.

For the quantitative approach, Ashland makes various estimates and assumptions in determining the estimated fair value of each reporting unit using a combination of discounted cash flow models and valuations based on earnings multiples for guideline public companies in each reporting unit’s industry peer group, when externally quoted market prices are not readily available. Discounted cash flow models are highly reliant on various assumptions, including projected business results and future industry direction, long-term growth factors and weighted-average cost of capital. Significant management judgement is involved in estimating these variables, and they include inherent uncertainties since they are forecasting future events. Ashland performs sensitivity analyses by using a range of inputs to confirm reasonableness of these estimates. Additionally, Ashland compares the indicated equity value to Ashland’s market capitalization, and implied control premium/discount, to determine if the estimated enterprise value is reasonable compared to external market indicators. If this comparison indicates that a reporting unit’s estimated fair value is less than its carrying value, it is adjusted to its calculated fair value and the adjustment represents the impairment charge.

Ashland performed its annual goodwill impairment test using the quantitative approach as of July 1, 2019 and concluded that the reporting unit fair values far exceeded their carrying values. No impairment existed as of that date.

Ashland reviews these intangible assets for possible impairment annually or whenever events or changes in circumstances indicate that carrying amounts may not be recoverable. If the carrying value of an individual indefinite-lived intangible asset exceeds its fair value, the asset is written down to its fair value and the amount of the write-down is the impairment charge. Similar to its annual assessment for goodwill, Ashland performs either a qualitative or quantitative test for impairment.

If a quantitative analysis is performed, Ashland tests these assets using a “relief-from-royalty” valuation method to determine the fair value. Significant assumptions inherent in the valuation methodologies include, but are not limited to, future projected business results, growth rates, the weighted-average cost of capital for a market participant, and royalty and discount rates. In conjunction with the July 1 annual assessment of indefinite-lived intangible assets, Ashland’s models did not indicate any impairment, as each indefinite-lived intangible asset’s fair value exceeded their carrying values.

Ashland performed its annual other intangibles impairment test using the quantitative approach as of July 1, 2019 and concluded that the assets fair values far exceeded their carrying values. No impairment existed as of that date.

Ashland’s assessment of an impairment on any of these assets classified currently as having indefinite lives, including goodwill, could change in future periods if significant events happen and/or circumstances change that effect the previously mentioned assumptions such as: a significant change in projected business result, a divestiture decision, increase in Ashland’s weighted-average cost of capital rates, decrease in growth rates or assumptions, economic deterioration that is more severe or of a longer duration than anticipated, or another significant economic event.