Consolidated Statements of Income (Parenthetical) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Income Statement [Abstract]
Earned premiums, net	$ 318.3	$ 459.0	$ 471.2
Net investment income, affiliates	4.9	4.9	4.9
Other income, affiliates	2.6	2.3	2.3
Losses and loss expenses, net affiliates	180.5	379.4	383.8
Net Acquisition and Operating Expenses	108.7	160.7	154.6
Interest Expense Debt To Affiliates	$ 1.0	$ 0.8	$ 0.7