Held for Sale and Discontinued Operations - Narrative (Details) - USD ($) $ in Millions		12 Months Ended
	May 12, 2022	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2018
Discontinued Operations
Total assets		$ 7,389.3	$ 7,000.7
Other Operations
Discontinued Operations
Liabilities held for sale - NSM Group		0.0	495.3
Total assets		2,018.7	2,201.8
Assets held for sale - Other		0.0	16.1
Sirius Group
Discontinued Operations
Gain (loss) on sale of discontinued operations		$ 0.0	18.7	$ (2.3)
Sirius Group | Discontinued Operations, Disposed of by Sale
Discontinued Operations
Gain (loss) on sale of discontinued operations			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
Other Operations | Discontinued Operations, Disposed of by Sale
Discontinued Operations
Proceeds from sale of segment	$ 19.5
Gain on sale of segment	$ 3.7
Other Operations | Disposal Group, Held-for-sale, Not Discontinued Operations
Discontinued Operations
Total assets			$ 16.1