Condensed Consolidated Statements of Income (Parenthetical) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Income Statement [Abstract]
Earned premiums, ceded to affiliates	$ 215.2	$ 215.2	$ 647.4	$ 639.0
Net investment income, from affiliate	1.3	1.3	3.7	3.7
Losses and loss expenses, ceded to affiliates	131.6	137.9	417.3	434.0
Interest expense, affiliates	$ 0.2	$ 0.1	$ 0.5	$ 0.5