Significant Transactions - NSM (Details) - USD ($) $ in Millions		3 Months Ended		9 Months Ended
	Aug. 01, 2022	Sep. 30, 2022	Sep. 30, 2021	Sep. 30, 2022	Sep. 30, 2021
Other Significant Noncash Transactions [Line Items]
Net gain (loss) from sale of discontinued operations, net of tax - Sirius Group				$ 886.8	$ 18.7
Net gain (loss) from foreign currency translation from sale of discontinued operations, net of tax - NSM Group		$ 2.9	$ 0.0	2.9	0.0
NSM Insurance Group
Other Significant Noncash Transactions [Line Items]
Net gain (loss) from sale of discontinued operations, net of tax - Sirius Group		$ 886.8	$ 0.0	$ 886.8	$ 0.0
Discontinued Operations, Disposed of by Sale | NSM Insurance Group
Other Significant Noncash Transactions [Line Items]
Transaction value	$ 1,400.0
Gain on transaction	875.7
Net gain (loss) from sale of discontinued operations, net of tax - Sirius Group	886.8
Net gain (loss) from foreign currency translation from sale of discontinued operations, net of tax - NSM Group	2.9
Compensation and other costs	$ 14.0