Condensed Consolidated Statements of Income (Parenthetical) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Income Statement [Abstract]
Earned premiums, from affiliates	$ 69.3	$ 55.7	$ 189.2	$ 168.5
Net investment income, from affiliate	0.7	0.7	2.1	2.3
Losses and loss expenses, from affiliates	48.7	24.2	132.8	125.1
Net Acquisition and Operating Expenses, from affiliates	24.2	17.6	65.9	54.5
Interest Expense Debt To Affiliates	$ 0.1	$ 0.2	$ 0.6	$ 0.7