Significant accounting policies - Narrative (Details) $ in Millions	12 Months Ended
Dec. 31, 2022 USD ($) segment	Dec. 31, 2021 USD ($)	Dec. 31, 2020 USD ($)
Accounting Policies [Abstract]
VOBA carrying value	$ 0.0	$ 50.0
Premium deficiency	0.0
Unrealized foreign currency translation losses	$ 5.0	$ 0.2	$ 0.0
Number of operating segments \| segment	2

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- References

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Number of operating segments. An operating segment is a component of an enterprise: (a) that engages in business activities from which it may earn revenues and incur expenses (including revenues and expenses relating to transactions with other components of the same enterprise), (b) whose operating results are regularly reviewed by the enterprise's chief operating decision maker to make decisions about resources to be allocated to the segment and assess its performance, and (c) for which discrete financial information is available. An operating segment may engage in business activities for which it has yet to earn revenues, for example, start-up operations may be operating segments before earning revenues.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
-SubTopic 10
-Section 50
-Paragraph 18
-URI https://asc.fasb.org/extlink&oid=126901519&loc=d3e8672-108599

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Amount after tax and reclassification adjustments of gain (loss) on foreign currency translation adjustments, foreign currency transactions designated and effective as economic hedges of a net investment in a foreign entity and intra-entity foreign currency transactions that are of a long-term-investment nature.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 220
-SubTopic 10
-Section 45
-Paragraph 10A
-Subparagraph (a)
-URI https://asc.fasb.org/extlink&oid=126968391&loc=SL7669646-108580

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Amount, after accumulated amortization, of present value of future profits of insurance contract acquired in business combination.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 20
-Section S99
-Paragraph 2
-URI https://asc.fasb.org/extlink&oid=122135039&loc=d3e569990-122904

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-03.10)
-URI https://asc.fasb.org/extlink&oid=126734703&loc=d3e572229-122910

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