Goodwill and other identifiable intangible assets - Schedule of Intangible Assets (Details) - USD ($) $ in Millions	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Finite-Lived Intangible Assets
Gross	$ 23.4	$ 21.7	$ 21.5
Accumulated amortization	(9.7)	(8.9)
Net	13.7	12.8
Customer relationships
Finite-Lived Intangible Assets
Gross	15.2	13.4	13.4
Accumulated amortization	(5.7)	(5.2)
Net	9.5	8.2
Technology and trading related
Finite-Lived Intangible Assets
Gross	8.2	8.3	$ 8.1
Accumulated amortization	(4.0)	(3.7)
Net	$ 4.2	$ 4.6

Accumulated amount of amortization of assets, excluding financial assets and goodwill, lacking physical substance with a finite life.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 350
-SubTopic 30
-Section 50
-Paragraph 2
-Subparagraph (a)(1)
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Amount before amortization of assets, excluding financial assets and goodwill, lacking physical substance with a finite life.

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Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 928
-SubTopic 340
-Section 50
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=6473545&loc=d3e61844-108004

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Amount after amortization of assets, excluding financial assets and goodwill, lacking physical substance with a finite life.

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Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 926
-SubTopic 20
-Section 50
-Paragraph 5
-URI http://asc.fasb.org/extlink&oid=120154696&loc=d3e54445-107959

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