Intangible Assets

Indefinite-lived intangible assets are tested and reviewed annually for impairment during the fourth quarter or whenever there is a significant change in events or circumstances that indicate that the fair value of the asset may be less than the carrying amount of the asset. All other intangible assets with finite useful lives are amortized on a straight-line basis over their estimated useful lives.

The gross amount of the Company’s intangible assets and related accumulated amortization were as follows:



	September 30, 2017							December 31, 2016
In millions	Gross carrying amount		Accumulated amortization			Net carrying amount		Gross carrying amount		Accumulated amortization			Net carrying amount
Completed technologies/patents	$	208.9	$	(175.0	)	$	33.9	$	203.0	$	(165.6	)	$	37.4
Customer relationships	2,063.0		(1,025.6		)	1,037.4		2,008.9		(926.1		)	1,082.8
Other	61.9		(49.3		)	12.6		61.1		(48.5		)	12.6
Total finite-lived intangible assets	2,333.8		(1,249.9		)	1,083.9		2,273.0		(1,140.2		)	1,132.8
Trademarks (indefinite-lived)	2,657.0		—			2,657.0		2,652.3		—			2,652.3
Total	$	4,990.8	$	(1,249.9	)	$	3,740.9	$	4,925.3	$	(1,140.2	)	$	3,785.1

Intangible asset amortization expense was $33.3 million and $33.0 million for the three months ended September 30, 2017 and 2016, respectively. Intangible asset amortization expense was $98.1 million and $99.1 million for the nine months ended September 30, 2017 and 2016, respectively.