Investments (Details 12) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012	Dec. 31, 2012
Commercial mortgage loans
Impaired mortgage loans
Recorded investment in impaired mortgage loans	$ 40.2		$ 40.2		$ 27.3
Unpaid principal balance of impaired mortgage loans	46.6		46.6		29.7
Related allowance for impaired mortgage loans	8.5		8.5		2.4
Average investment in impaired mortgage loans	34.8	47.2	33.7	71.4
Interest income recognized on impaired mortgage loans	0.2	0.6	0.4	2.6
Brick and mortar
Impaired mortgage loans
Recorded investment in impaired mortgage loans with no related allowance	9.5		9.5		22.9
Recorded investment in impaired mortgage loans with related allowance	30.7		30.7		4.4
Unpaid principal balance of impaired mortgage loans with no related allowance	16.0		16.0		25.3
Unpaid principal balance of impaired mortgage loans with related allowance	30.6		30.6		4.4
Related allowance for impaired mortgage loans	8.5		8.5		2.4
Average investment in impaired mortgage loans with no related allowance	6.4	27.0	16.2	5.3
Average investment in impaired mortgage loans with related allowance	28.4	20.2	17.5	66.1
Interest income recognized on impaired mortgage loans with no related allowance	0.1	0.1	0.2	1.1
Interest income recognized on impaired mortgage loans with related allowance	0.1	0.5	0.2	1.5
Residential mortgage loans
Impaired mortgage loans
Recorded investment in impaired mortgage loans	34.7		34.7		39.7
Unpaid principal balance of impaired mortgage loans	35.0		35.0		36.4
Related allowance for impaired mortgage loans	10.4		10.4		10.4
Average investment in impaired mortgage loans	35.7	33.5	37.2	31.5
Interest income recognized on impaired mortgage loans	0.4	0.2	0.9	0.8
Home equity
Impaired mortgage loans
Recorded investment in impaired mortgage loans with related allowance	19.8		19.8		20.8
Unpaid principal balance of impaired mortgage loans with related allowance	20.2		20.2		20.7
Related allowance for impaired mortgage loans	9.3		9.3		9.1
Average investment in impaired mortgage loans with related allowance	20.2	20.2	20.3	18.7
Interest income recognized on impaired mortgage loans with related allowance	0.4	0.2	0.8	0.7
First liens
Impaired mortgage loans
Recorded investment in impaired mortgage loans with no related allowance	6.0		6.0		9.7
Recorded investment in impaired mortgage loans with related allowance	8.9		8.9		9.2
Unpaid principal balance of impaired mortgage loans with no related allowance	6.0		6.0		6.6
Unpaid principal balance of impaired mortgage loans with related allowance	8.8		8.8		9.1
Related allowance for impaired mortgage loans	1.1		1.1		1.3
Average investment in impaired mortgage loans with no related allowance	6.2	5.2	7.9	4.6
Average investment in impaired mortgage loans with related allowance	9.3	8.1	9.0	8.2
Interest income recognized on impaired mortgage loans with related allowance			$ 0.1	$ 0.1