Goodwill and Other Identifiable Intangible Assets

The changes in the carrying amount of goodwill by reportable segment were as follows:



In millions	December 31, 2017		Foreign currency translation/other			September 30, 2018
Aquatic Systems	$	973.1	$	(6.0	)	$	967.1
Filtration Solutions	472.1		(7.9		)	464.2
Flow Technologies	667.6		(1.9		)	665.7
Total goodwill	$	2,112.8	$	(15.8	)	$	2,097.0

Identifiable intangible assets consisted of the following:



	September 30, 2018							December 31, 2017
In millions	Cost		Accumulated amortization			Net		Cost		Accumulated amortization			Net
Definite-life intangibles
Customer relationships	$	353.3	$	(245.5	)	$	107.8	$	360.9	$	(229.9	)	$	131.0
Trade names	0.4		(0.4		)	—		1.5		(1.4		)	0.1
Proprietary technology and patents	88.0		(68.2		)	19.8		117.0		(89.3		)	27.7
Total definite-life intangibles	441.7		(314.1		)	127.6		479.4		(320.6		)	158.8
Indefinite-life intangibles
Trade names	161.8		—			161.8		163.0		—			163.0
Total intangibles	$	603.5	$	(314.1	)	$	289.4	$	642.4	$	(320.6	)	$	321.8

Identifiable intangible asset amortization expense was $8.6 million and $9.2 million for the three months ended September 30, 2018 and 2017, respectively, and $27.0 million and $27.2 million for the nine months ended September 30, 2018 and 2017, respectively.

Estimated future amortization expense for identifiable intangible assets during the remainder of 2018 and the next five years is as follows:



	Q4
In millions	2018		2019		2020		2021		2022		2023
Estimated amortization expense	$	8.3	$	28.0	$	22.9	$	17.6	$	10.3	$	7.9