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Held for Sale and Discontinued Operations - Narrative (Details) - Sirius Group - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2018	Dec. 31, 2020
Discontinued Operations
Net gain (loss) from sale of discontinued operations, net of tax	$ 0.0	$ 0.0	$ 18.7
Discontinued Operations, Disposed of by Sale
Discontinued Operations
Net gain (loss) from sale of discontinued operations, net of tax			17.6	$ (17.3)
Liabilities held for sale - NSM Group					$ 18.7
Net (income) loss from discontinued operations attributable to non-controlling interests			$ 1.1