Investments (Details 9) (USD $) In Millions, unless otherwise specified																																							3 Months Ended	12 Months Ended
	Mar. 31, 2014	Dec. 31, 2013	Mar. 31, 2013	Mar. 31, 2014 Commercial mortgage loans	Dec. 31, 2013 Commercial mortgage loans	Mar. 31, 2013 Commercial mortgage loans	Mar. 31, 2014 Commercial mortgage loans A- and above	Dec. 31, 2013 Commercial mortgage loans A- and above	Mar. 31, 2014 Commercial mortgage loans BBB+ thru BBB-	Dec. 31, 2013 Commercial mortgage loans BBB+ thru BBB-	Mar. 31, 2014 Commercial mortgage loans BB+ thru BB-	Dec. 31, 2013 Commercial mortgage loans BB+ thru BB-	Mar. 31, 2014 Commercial mortgage loans B+ and below	Dec. 31, 2013 Commercial mortgage loans B+ and below	Mar. 31, 2014 Brick and mortar	Dec. 31, 2013 Brick and mortar	Mar. 31, 2014 Brick and mortar A- and above	Dec. 31, 2013 Brick and mortar A- and above	Mar. 31, 2014 Brick and mortar BBB+ thru BBB-	Dec. 31, 2013 Brick and mortar BBB+ thru BBB-	Mar. 31, 2014 Brick and mortar BB+ thru BB-	Dec. 31, 2013 Brick and mortar BB+ thru BB-	Mar. 31, 2014 Brick and mortar B+ and below	Dec. 31, 2013 Brick and mortar B+ and below	Mar. 31, 2014 Credit tenant loans	Dec. 31, 2013 Credit tenant loans	Mar. 31, 2014 Credit tenant loans A- and above	Dec. 31, 2013 Credit tenant loans A- and above	Mar. 31, 2014 Credit tenant loans BBB+ thru BBB-	Dec. 31, 2013 Credit tenant loans BBB+ thru BBB-	Dec. 31, 2013 Credit tenant loans BB+ thru BB-	Mar. 31, 2014 Credit tenant loans B+ and below	Dec. 31, 2013 Credit tenant loans B+ and below	Mar. 31, 2014 Residential mortgage loans	Dec. 31, 2013 Residential mortgage loans	Mar. 31, 2013 Residential mortgage loans	Mar. 31, 2014 Residential mortgage loans Performing	Dec. 31, 2013 Residential mortgage loans Performing	Mar. 31, 2014 Residential mortgage loans Nonperforming	Dec. 31, 2013 Residential mortgage loans Nonperforming	Mar. 31, 2014 Home equity	Dec. 31, 2013 Home equity	Mar. 31, 2014 Home equity Performing	Dec. 31, 2013 Home equity Performing	Mar. 31, 2014 Home equity Nonperforming	Dec. 31, 2013 Home equity Nonperforming	Mar. 31, 2014 First liens	Dec. 31, 2013 First liens	Mar. 31, 2014 First liens Performing	Dec. 31, 2013 First liens Performing	Mar. 31, 2014 First liens Nonperforming	Dec. 31, 2013 First liens Nonperforming
Mortgage loan credit quality disclosures
Mortgage loans, Total amortized cost	$ 11,544.9	$ 11,603.4	$ 11,667.4	$ 10,299.0	$ 10,327.7	$ 10,286.5	$ 8,391.3	$ 8,286.4	$ 1,612.8	$ 1,713.7	$ 167.7	$ 155.5	$ 127.2	$ 172.1	$ 9,887.8	$ 9,881.1	$ 8,204.0	$ 8,091.9	$ 1,390.8	$ 1,463.7	$ 167.7	$ 155.4	$ 125.3	$ 170.1	$ 411.2	$ 446.6	$ 187.3	$ 194.5	$ 222.0	$ 250.0	$ 0.1	$ 1.9	$ 2.0	$ 1,245.9	$ 1,275.7	$ 1,380.9	$ 1,212.4	$ 1,240.4	$ 33.5	$ 35.3	$ 377.1	$ 394.9	$ 361.0	$ 378.3	$ 16.1	$ 16.6	$ 868.8	$ 880.8	$ 851.4	$ 862.1	$ 17.4	$ 18.7
Mortgage loans, Days delinquent to be considered nonperforming																																							90 days	90 days