Quarterly financial results (Unaudited) - Narrative (Details) - Sirius Group - USD ($) $ in Millions		3 Months Ended
Feb. 26, 2021	Mar. 31, 2021
Business Acquisition [Line Items]
Bargain purchase gain	$ 50.4	$ 50.4
Revision of prior period, error correction, adjustment
Business Acquisition [Line Items]
Bargain purchase gain		37.5
As previously reported
Business Acquisition [Line Items]
Bargain purchase gain		$ 12.9

In a business combination in which the amount of net identifiable assets acquired and liabilities assumed exceeds the aggregate consideration transferred or to be transferred (as defined), this element represents the amount of gain recognized by the entity.

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