Investments Fixed Maturity Securities by Type (Details) (USD $) In Millions, unless otherwise specified	Jun. 30, 2012	Dec. 31, 2011
Schedule of Available-for-sale Securities [Line Items]
Fixed maturitiy securities (amortized costs)	$ 7,837.8	$ 7,884.6
Available for sale, Fixed maturity securities	8,387.1	8,393.2
U.S. & Canadian Governments [Member]
Schedule of Available-for-sale Securities [Line Items]
Fixed maturitiy securities (amortized costs)	1,042.0	1,104.0
Fixed maturity securities, gross unrealized gains	72.2	78.3
Fixed maturity securities, gross unrealized losses	0.1	0.1
Available for sale, Fixed maturity securities	1,114.1	1,182.1
Tax-exempt [Member]
Schedule of Available-for-sale Securities [Line Items]
Fixed maturitiy securities (amortized costs)	498.9	597.1
Fixed maturity securities, gross unrealized gains	17.6	23.4
Fixed maturity securities, gross unrealized losses	0	0
Available for sale, Fixed maturity securities	516.5	620.5
Corporate [Member]
Schedule of Available-for-sale Securities [Line Items]
Fixed maturitiy securities (amortized costs)	6,296.8	6,183.5
Fixed maturity securities, gross unrealized gains	463.4	414.1
Fixed maturity securities, gross unrealized losses	3.8	7.0
Available for sale, Fixed maturity securities	6,756.4	6,590.5
Fixed Maturity Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Fixed maturitiy securities (amortized costs)	7,837.8	7,884.6
Fixed maturity securities, gross unrealized gains	553.4	515.9
Fixed maturity securities, gross unrealized losses	4.0	7.2
Available for sale, Fixed maturity securities	$ 8,387.1	$ 8,393.2

For an unclassified balance sheet, total of debt securities categorized neither as held-to-maturity nor trading.

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Reference 4: http://www.xbrl.org/2003/role/presentationRef

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-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

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+ Details