Investments (Details 12) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011	Dec. 31, 2011
Commercial mortgage loans
Impaired mortgage loans
Recorded investment in impaired mortgage loans	$ 28.7		$ 28.7		$ 114.0
Unpaid principal balance of impaired mortgage loans	31.2		31.2		114.3
Related allowance for impaired mortgage loans	4.8		4.8		16.3
Average investment in impaired mortgage loans	47.2	67.4	27.5	60.1
Interest income recognized on impaired mortgage loans	0.6	0.5	2.6	1.6
Brick and mortar
Impaired mortgage loans
Recorded investment in impaired mortgage loans with no related allowance	10.6		10.6
Recorded investment in impaired mortgage loans with related allowance	18.1		18.1		114.0
Unpaid principal balance of impaired mortgage loans with no related allowance	10.9		10.9		0.3
Unpaid principal balance of impaired mortgage loans with related allowance	20.3		20.3		114.0
Related allowance for impaired mortgage loans	4.8		4.8		16.3
Average investment in impaired mortgage loans with no related allowance	27.0	45.0	5.3	31.6
Average investment in impaired mortgage loans with related allowance	20.2	22.4	22.2	28.5
Interest income recognized on impaired mortgage loans with no related allowance	0.1	0.2	1.1	0.7
Interest income recognized on impaired mortgage loans with related allowance	0.5	0.3	1.5	0.9
Residential mortgage loans
Impaired mortgage loans
Recorded investment in impaired mortgage loans	35.3		35.3		27.4
Unpaid principal balance of impaired mortgage loans	34.9		34.9		26.9
Related allowance for impaired mortgage loans	7.8		7.8		3.2
Average investment in impaired mortgage loans	33.5	26.1	31.5	26.6
Interest income recognized on impaired mortgage loans	0.2	0.2	0.8	0.6
Home equity
Impaired mortgage loans
Recorded investment in impaired mortgage loans with related allowance	22.9		22.9		14.5
Unpaid principal balance of impaired mortgage loans with related allowance	22.6		22.6		14.2
Related allowance for impaired mortgage loans	6.7		6.7		1.9
Average investment in impaired mortgage loans with related allowance	20.2	12.6	18.7	12.4
Interest income recognized on impaired mortgage loans with related allowance	0.2	0.2	0.7	0.5
First liens
Impaired mortgage loans
Recorded investment in impaired mortgage loans with no related allowance	4.9		4.9		4.4
Recorded investment in impaired mortgage loans with related allowance	7.5		7.5		8.5
Unpaid principal balance of impaired mortgage loans with no related allowance	4.8		4.8		4.2
Unpaid principal balance of impaired mortgage loans with related allowance	7.5		7.5		8.5
Related allowance for impaired mortgage loans	1.1		1.1		1.3
Average investment in impaired mortgage loans with no related allowance	5.2	4.0	4.6	4.5
Average investment in impaired mortgage loans with related allowance	8.1	9.5	8.2	9.7
Interest income recognized on impaired mortgage loans with related allowance			$ 0.1	$ 0.1