Condensed Consolidated Statements of Income (Parenthetical) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Income Statement [Abstract]
Earned premiums, from affiliates	$ 71.9	$ 115.3	$ 251.1	$ 349.0
Net investment income, from affiliate	1.3	1.3	3.7	3.7
Losses and loss expenses, from affiliates	34.7	128.9	105.4	298.8
Net Acquisition and Operating Expenses, from affiliates	(26.8)	78.9	52.3	217.0
Interest Expense Debt To Affiliates	$ 0.2	$ 0.2	$ 0.7	$ 0.6