Condensed Consolidated Statements of Income (Parenthetical) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Income Statement [Abstract]
Earned premiums, from affiliates	$ 115.3	$ 121.4	$ 348.2	$ 352.4
Net investment income, from affiliate	1.3	1.3	3.7	3.7
Losses and loss expenses, from affiliates	128.9	100.9	298.5	281.4
Net Acquisition and Operating Expenses, from affiliates	78.9	73.9	231.0	217.0
Interest Expense Debt To Affiliates	$ 0.2	$ 0.2	$ 0.6	$ 0.6