Investments Gross Unrealized Losses and Fair Value (Details) (USD $) In Millions, unless otherwise specified	Jun. 30, 2012	Dec. 31, 2011
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, continuous unrealized loss position, less than twelve months, Fair Value	$ 308.9	$ 539.1
Available-for-sale Securities, continuous unrealized loss position, less than 12 months, Unrealized Losses	2.7	11.5
Available-for-sale Securities, continuous unrealized loss position, twelve months or longer, Fair Value	12.3	2.4
Available-for-sale Securities, continuous unrealized loss position, 12 months or longer, Unrealized Losses	1.3	0.3
Available-for-sale Securities, continuous unrealized loss position, Fair Value	321.2	541.5
Available-for-sale Securities, continuous unrealized loss position, Unrealized Losses	4.0	11.9
U.S. & Canadian Governments [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, continuous unrealized loss position, less than twelve months, Fair Value	32.4	35.5
Available-for-sale Securities, continuous unrealized loss position, less than 12 months, Unrealized Losses	0.1	0.1
Available-for-sale Securities, continuous unrealized loss position, twelve months or longer, Fair Value	0	0
Available-for-sale Securities, continuous unrealized loss position, 12 months or longer, Unrealized Losses	0	0
Available-for-sale Securities, continuous unrealized loss position, Fair Value	32.4	35.5
Available-for-sale Securities, continuous unrealized loss position, Unrealized Losses	0.1	0.1
Tax-exempt [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, continuous unrealized loss position, less than twelve months, Fair Value	2.4	2.1
Available-for-sale Securities, continuous unrealized loss position, less than 12 months, Unrealized Losses	0	0
Available-for-sale Securities, continuous unrealized loss position, twelve months or longer, Fair Value	0	0.6
Available-for-sale Securities, continuous unrealized loss position, 12 months or longer, Unrealized Losses	0	0
Available-for-sale Securities, continuous unrealized loss position, Fair Value	2.4	2.7
Available-for-sale Securities, continuous unrealized loss position, Unrealized Losses	0	0
Corporate [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, continuous unrealized loss position, less than twelve months, Fair Value	269.4	402.9
Available-for-sale Securities, continuous unrealized loss position, less than 12 months, Unrealized Losses	2.5	6.7
Available-for-sale Securities, continuous unrealized loss position, twelve months or longer, Fair Value	12.3	1.7
Available-for-sale Securities, continuous unrealized loss position, 12 months or longer, Unrealized Losses	1.3	0.2
Available-for-sale Securities, continuous unrealized loss position, Fair Value	281.8	404.7
Available-for-sale Securities, continuous unrealized loss position, Unrealized Losses	3.8	7.0
Fixed Maturity Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, continuous unrealized loss position, less than twelve months, Fair Value	304.3	440.6
Available-for-sale Securities, continuous unrealized loss position, less than 12 months, Unrealized Losses	2.6	7.0
Available-for-sale Securities, continuous unrealized loss position, twelve months or longer, Fair Value	12.3	2.3
Available-for-sale Securities, continuous unrealized loss position, 12 months or longer, Unrealized Losses	1.3	0.2
Available-for-sale Securities, continuous unrealized loss position, Fair Value	316.7	443.0
Available-for-sale Securities, continuous unrealized loss position, Unrealized Losses	4.0	7.2
Equity Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, continuous unrealized loss position, less than twelve months, Fair Value	4.5	98.4
Available-for-sale Securities, continuous unrealized loss position, less than 12 months, Unrealized Losses	0	4.5
Available-for-sale Securities, continuous unrealized loss position, twelve months or longer, Fair Value	0	0
Available-for-sale Securities, continuous unrealized loss position, 12 months or longer, Unrealized Losses	0	0
Available-for-sale Securities, continuous unrealized loss position, Fair Value	4.5	98.5
Available-for-sale Securities, continuous unrealized loss position, Unrealized Losses	$ 0	$ 4.6