Business Segments - Earned Premiums by Product Line (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Entity-Wide Information, Revenue from External Customer [Line Items]
Earned Premiums, Life	$ 95.4	$ 95.5	$ 191.1	$ 189.9
Earned Premiums, Accident and Health	39.5	36.7	78.6	73.6
Total Earned Premiums	582.5	553.7	1,145.9	1,099.7
Personal Automobile [Member]
Entity-Wide Information, Revenue from External Customer [Line Items]
Earned Premiums, Property and Casualty	339.1	310.3	659.8	613.6
Homeowners [Member]
Entity-Wide Information, Revenue from External Customer [Line Items]
Earned Premiums, Property and Casualty	66.6	67.6	132.9	135.7
Other Personal Property and Casualty Insurance [Member]
Entity-Wide Information, Revenue from External Customer [Line Items]
Earned Premiums, Property and Casualty	29.2	30.2	58.1	60.0
Commercial Automobile [Member]
Entity-Wide Information, Revenue from External Customer [Line Items]
Earned Premiums, Property and Casualty	$ 12.7	$ 13.4	$ 25.4	$ 26.9