Intangible assets - Narrative (Details) - USD ($) $ in Millions	3 Months Ended
Mar. 28, 2020	Mar. 30, 2019
Goodwill and Intangible Assets Disclosure [Abstract]
Amortization expense	$ 32.2	$ 32.6
Intangible assets, foreign currency translation gain (loss)	$ (38.4)	$ 3.3

The aggregate expense charged against earnings to allocate the cost of intangible assets (nonphysical assets not used in production) in a systematic and rational manner to the periods expected to benefit from such assets. As a noncash expense, this element is added back to net income when calculating cash provided by or used in operations using the indirect method.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
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Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
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Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
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