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Commitments and Contingencies (Details) - USD ($) $ in Millions	3 Months Ended	9 Months Ended
	Sep. 30, 2019	Sep. 30, 2019	Dec. 31, 2019	Jun. 28, 2019	Dec. 31, 2018
American International Group \| NSM Insurance HoldCo, LLC
Loss Contingencies [Line Items]
Intangible assets acquired				$ 82.5
Sirius Group \| Swedish Tax Authority \| Sirius Group
Loss Contingencies [Line Items]
Contingent liability	$ 15.7	$ 15.7			$ 17.3
Change in contingent liability	$ 0.9	$ (1.6)
Scenario, Forecast \| American International Group \| NSM Insurance HoldCo, LLC
Loss Contingencies [Line Items]
Purchase Obligation			$ 82.5