Condensed Consolidated Statements of Income (Parenthetical) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Income Statement [Abstract]
Earned premiums, from affiliates	$ 98.0	$ 114.8
Net investment income, from affiliate	1.2	1.2
Losses and loss expenses, from affiliates	46.2	86.2
Net Acquisition and Operating Expenses, from affiliates	43.6	80.3
Interest Expense Debt To Affiliates	$ 0.2	$ 0.2