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Held for Sale and Discontinued Operations - (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018	Dec. 31, 2018
Discontinued Operations [Line Items}
Gain (loss) from sale of discontinued operations, net of tax	$ 0.0	$ 0.0	$ 0.7	$ 0.1
Connecticut \| Discontinued Operations, Held-for-sale
Discontinued Operations [Line Items}
Assets held for sale	2.8		2.8		$ 3.3
Swedish Tax Authority \| Discontinued Operations \| Sirius Group
Discontinued Operations [Line Items}
Gain (loss) from sale of discontinued operations, net of tax				$ 0.1
Sirius Group \| Swedish Tax Authority \| Sirius Group
Discontinued Operations [Line Items}
Contingent liability	16.6		16.6		$ 17.3
Change in contingent liability	$ (0.7)		$ (0.7)