Summary of significant accounting policies - Stock-based compensation (Details) - USD ($) $ in Millions		6 Months Ended	12 Months Ended
Jul. 24, 2020	Jun. 30, 2020	Dec. 31, 2021	Dec. 31, 2018
Accounting Policies [Abstract]
Threshold cash return on investment upon termination event to determine vesting of performance shares	$ 1,515.0		$ 1,515.0	$ 1,515.0
Award expiration period			10 years
Fair value after plan modification		$ 33.0

Period from grant date that an equity-based award expires, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (a)(2)
-URI http://asc.fasb.org/extlink&oid=120381028&loc=d3e5070-113901

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Data Type:	xbrli:durationItemType
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Period Type:	duration