Investments (Details 12) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2012	Mar. 31, 2011	Dec. 31, 2011
Commercial mortgage loans
Impaired mortgage loans
Recorded investment in impaired mortgage loans	$ 135.6		$ 114.0
Unpaid principal balance of impaired mortgage loans	150.5		114.3
Related allowance for impaired mortgage loans	6.2		16.3
Average investment in impaired mortgage loans	124.8	58.2
Interest income recognized on impaired mortgage loans	1.1	0.5
Brick and mortar | Impaired Mortgage Loans with No Related Allowance
Impaired mortgage loans
Recorded investment in impaired mortgage loans	95.3
Unpaid principal balance of impaired mortgage loans	108.3		0.3
Average investment in impaired mortgage loans	47.7	23.2
Interest income recognized on impaired mortgage loans	1.1	0.3
Brick and mortar | Impaired Mortgage Loans with Related Allowance
Impaired mortgage loans
Recorded investment in impaired mortgage loans	40.3		114.0
Unpaid principal balance of impaired mortgage loans	42.2		114.0
Related allowance for impaired mortgage loans	6.2		16.3
Average investment in impaired mortgage loans	77.1	35.0
Interest income recognized on impaired mortgage loans		0.2
Residential mortgage loans
Impaired mortgage loans
Recorded investment in impaired mortgage loans	31.4		27.4
Unpaid principal balance of impaired mortgage loans	30.9		26.9
Related allowance for impaired mortgage loans	4.6		3.2
Average investment in impaired mortgage loans	29.5	26.2
Interest income recognized on impaired mortgage loans	0.3	0.2
Home equity | Impaired Mortgage Loans with Related Allowance
Impaired mortgage loans
Recorded investment in impaired mortgage loans	16.4		14.5
Unpaid principal balance of impaired mortgage loans	16.1		14.2
Related allowance for impaired mortgage loans	3.1		1.9
Average investment in impaired mortgage loans	15.4	11.7
Interest income recognized on impaired mortgage loans	0.3	0.1
First liens | Impaired Mortgage Loans with No Related Allowance
Impaired mortgage loans
Recorded investment in impaired mortgage loans	6.2		4.4
Unpaid principal balance of impaired mortgage loans	6.1		4.2
Average investment in impaired mortgage loans	5.3	4.6
First liens | Impaired Mortgage Loans with Related Allowance
Impaired mortgage loans
Recorded investment in impaired mortgage loans	8.8		8.5
Unpaid principal balance of impaired mortgage loans	8.7		8.5
Related allowance for impaired mortgage loans	1.5		1.3
Average investment in impaired mortgage loans	8.8	9.9
Interest income recognized on impaired mortgage loans		$ 0.1