Investments Net Investment Income (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012	Jun. 30, 2011
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Gross investment income	$ 323.6	$ 391.4	$ 686.9	$ 745.2
Less: investment expense	(11.7)	(10.7)	(23.0)	(21.5)
Net investment income	311.9	380.7	663.9	723.7
Fixed maturities
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Gross investment income	303.7	316.0	608.0	612.6
Equity securities, available-for-sale
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Gross investment income	3.0	4.8	4.1	8.5
Mortgage loans on real estate
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Gross investment income	37.5	29.1	71.1	55.6
Policy loans
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Gross investment income	3.3	3.3	6.6	6.5
Short-term investments and cash equivalents
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Gross investment income	0.3	0.4	0.5	0.7
Other
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Gross investment income	$ (24.2)	$ 37.8	$ (3.4)	$ 61.3