Business Segments - Earned Premiums by Product Line (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011
Entity-Wide Information, Revenue from External Customer [Line Items]
Earned Premiums, Life	$ 98.4	$ 98.0	$ 296.0	$ 297.1
Earned Premiums, Accident and Health	41.3	41.9	124.2	124.6
Earned Premiums, Total	527.3	543.0	1,586.3	1,637.1
Personal Lines [Member]
Entity-Wide Information, Revenue from External Customer [Line Items]
Earned Premiums, Property and Casualty	376.6	393.0	1,134.4	1,185.6
Automobile [Member]
Entity-Wide Information, Revenue from External Customer [Line Items]
Earned Premiums, Property and Casualty	261.3	281.4	794.6	854.7
Homeowners [Member]
Entity-Wide Information, Revenue from External Customer [Line Items]
Earned Premiums, Property and Casualty	80.8	76.6	236.6	226.4
Other Personal Lines [Member]
Entity-Wide Information, Revenue from External Customer [Line Items]
Earned Premiums, Property and Casualty	34.5	35.0	103.2	104.5
Commercial Automobile [Member]
Entity-Wide Information, Revenue from External Customer [Line Items]
Earned Premiums, Property and Casualty	$ 11.0	$ 10.1	$ 31.7	$ 29.8