Condensed Consolidated Statements of Income (Parenthetical) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Income Statement [Abstract]
Earned premiums, from affiliates	$ 118.1	$ 117.6	$ 232.9	$ 231.0
Net investment income, from affiliate	1.2	1.2	2.4	2.4
Losses and loss expenses, from affiliates	83.4	86.8	169.6	180.5
Net Acquisition and Operating Expenses, from affiliates	71.8	68.4	152.1	138.9
Interest Expense Debt To Affiliates	$ 0.2	$ 0.2	$ 0.4	$ 0.4