Significant Transactions - NSM (Details) - USD ($) $ in Millions		3 Months Ended	9 Months Ended
Aug. 01, 2022	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Other Significant Transactions [Line Items]
Net gain (loss) from sale of discontinued operations, net of tax - NSM Group		$ 0.0	$ 886.8	$ 0.0	$ 886.8
Net gain (loss) from foreign currency translation from sale of discontinued operations, net of tax - NSM Group		$ 0.0	2.9	$ 0.0	2.9
Discontinued Operations, Disposed of by Sale \| NSM Insurance Group
Other Significant Transactions [Line Items]
Transaction value	$ 1,400.0
Net transaction gain	875.7
Net gain (loss) from sale of discontinued operations, net of tax - NSM Group	886.8		886.8		886.8
Net gain (loss) from foreign currency translation from sale of discontinued operations, net of tax - NSM Group	2.9		2.9		2.9
Compensation and other costs	$ 14.0		$ 15.7		$ 126.8

Amount after tax of gain (loss) not previously recognized resulting from the disposal of a discontinued operation.

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