Investments (Details 13) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Commercial mortgage loans
Impaired mortgage loans
Recorded investment in impaired mortgage loans	$ 114.0	$ 52.3	$ 120.7
Unpaid principal balance of impaired mortgage loans	114.3	58.6	120.5
Related allowance for impaired mortgage loans	16.3	9.1	43.8
Average investment in impaired mortgage loans	90.3	90.6	97.6
Interest income recognized on impaired mortgage loans	1.9	2.9	0.3
Brick and mortar | Impaired Mortgage Loans with No Related Allowance
Impaired mortgage loans
Recorded investment in impaired mortgage loans		22.5
Unpaid principal balance of impaired mortgage loans	0.3	28.9
Average investment in impaired mortgage loans	11.3	13.4
Interest income recognized on impaired mortgage loans	0.9	1.1
Brick and mortar | Impaired Mortgage Loans with Related Allowance
Impaired mortgage loans
Recorded investment in impaired mortgage loans	114.0	29.8
Unpaid principal balance of impaired mortgage loans	114.0	29.7
Related allowance for impaired mortgage loans	16.3	9.1
Average investment in impaired mortgage loans	79.0	77.2
Interest income recognized on impaired mortgage loans	1.0	1.8
Residential mortgage loans
Impaired mortgage loans
Recorded investment in impaired mortgage loans	27.4	26.8	13.5
Unpaid principal balance of impaired mortgage loans	26.9	26.3	18.0
Related allowance for impaired mortgage loans	3.2	5.3	7.3
Average investment in impaired mortgage loans	26.6	33.7	15.3
Interest income recognized on impaired mortgage loans	1.0
Home equity | Impaired Mortgage Loans with Related Allowance
Impaired mortgage loans
Recorded investment in impaired mortgage loans	14.5	11.5
Unpaid principal balance of impaired mortgage loans	14.2	11.2
Related allowance for impaired mortgage loans	1.9	2.3
Average investment in impaired mortgage loans	12.6	12.2
Interest income recognized on impaired mortgage loans	0.8
First liens | Impaired Mortgage Loans with No Related Allowance
Impaired mortgage loans
Recorded investment in impaired mortgage loans	4.4	5.3
Unpaid principal balance of impaired mortgage loans	4.2	5.2
Average investment in impaired mortgage loans	4.4	5.3
First liens | Impaired Mortgage Loans with Related Allowance
Impaired mortgage loans
Recorded investment in impaired mortgage loans	8.5	10.0
Unpaid principal balance of impaired mortgage loans	8.5	9.9
Related allowance for impaired mortgage loans	1.3	3.0
Average investment in impaired mortgage loans	9.6	16.2
Interest income recognized on impaired mortgage loans	$ 0.2