Condensed Consolidated Statements of Income (Parenthetical) (USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013
Income Statement [Abstract]
Earned premiums, ceded to affiliates	$ 216.8	$ 213.1	$ 432.2	$ 423.8
Net investment income, from affiliate	1.2	1.2	2.4	2.4
Losses and loss expenses, ceded to affiliates	143.5	164.4	285.7	296.2
Interest expense, affiliates	$ 0.1	$ 0.2	$ 0.3	$ 0.4