Investments (Details 10) (USD $) In Millions, unless otherwise specified																																								12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2012 Commercial mortgage loans	Dec. 31, 2011 Commercial mortgage loans	Dec. 31, 2010 Commercial mortgage loans	Dec. 31, 2012 Commercial mortgage loans A- and above	Dec. 31, 2011 Commercial mortgage loans A- and above	Dec. 31, 2012 Commercial mortgage loans BBB+ thru BBB-	Dec. 31, 2011 Commercial mortgage loans BBB+ thru BBB-	Dec. 31, 2012 Commercial mortgage loans BB+ thru BB-	Dec. 31, 2011 Commercial mortgage loans BB+ thru BB-	Dec. 31, 2012 Commercial mortgage loans B+ and below	Dec. 31, 2011 Commercial mortgage loans B+ and below	Dec. 31, 2012 Brick and mortar	Dec. 31, 2011 Brick and mortar	Dec. 31, 2012 Brick and mortar A- and above	Dec. 31, 2011 Brick and mortar A- and above	Dec. 31, 2012 Brick and mortar BBB+ thru BBB-	Dec. 31, 2011 Brick and mortar BBB+ thru BBB-	Dec. 31, 2012 Brick and mortar BB+ thru BB-	Dec. 31, 2011 Brick and mortar BB+ thru BB-	Dec. 31, 2012 Brick and mortar B+ and below	Dec. 31, 2011 Brick and mortar B+ and below	Dec. 31, 2012 Credit tenant loans	Dec. 31, 2011 Credit tenant loans	Dec. 31, 2012 Credit tenant loans A- and above	Dec. 31, 2011 Credit tenant loans A- and above	Dec. 31, 2012 Credit tenant loans BBB+ thru BBB-	Dec. 31, 2011 Credit tenant loans BBB+ thru BBB-	Dec. 31, 2012 Credit tenant loans BB+ thru BB-	Dec. 31, 2011 Credit tenant loans BB+ thru BB-	Dec. 31, 2012 Credit tenant loans B+ and below	Dec. 31, 2011 Credit tenant loans B+ and below	Dec. 31, 2012 Residential mortgage loans	Dec. 31, 2011 Residential mortgage loans	Dec. 31, 2010 Residential mortgage loans	Dec. 31, 2012 Residential mortgage loans Performing	Dec. 31, 2011 Residential mortgage loans Performing	Dec. 31, 2012 Residential mortgage loans Nonperforming	Dec. 31, 2011 Residential mortgage loans Nonperforming	Dec. 31, 2012 Home equity	Dec. 31, 2011 Home equity	Dec. 31, 2012 Home equity Performing	Dec. 31, 2011 Home equity Performing	Dec. 31, 2012 Home equity Nonperforming	Dec. 31, 2011 Home equity Nonperforming	Dec. 31, 2012 First liens	Dec. 31, 2011 First liens	Dec. 31, 2012 First liens Performing	Dec. 31, 2011 First liens Performing	Dec. 31, 2012 First liens Nonperforming	Dec. 31, 2011 First liens Nonperforming
Mortgage loan credit quality disclosures
Mortgage loans, Total amortized cost	$ 11,617.1	$ 10,829.3	$ 11,246.2	$ 10,235.1	$ 9,461.4	$ 9,689.6	$ 7,489.0	$ 5,991.1	$ 2,099.4	$ 2,351.1	$ 268.4	$ 420.1	$ 378.3	$ 699.1	$ 9,705.0	$ 8,891.8	$ 7,257.7	$ 5,682.5	$ 1,804.5	$ 2,112.3	$ 266.8	$ 403.7	$ 376.0	$ 693.3	$ 530.1	$ 569.6	$ 231.3	$ 308.6	$ 294.9	$ 238.8	$ 1.6	$ 16.4	$ 2.3	$ 5.8	$ 1,382.0	$ 1,367.9	$ 1,556.6	$ 1,337.6	$ 1,331.5	$ 44.4	$ 36.4	$ 495.7	$ 611.0	$ 472.6	$ 597.8	$ 23.1	$ 13.2	$ 886.3	$ 756.9	$ 865.0	$ 733.7	$ 21.3	$ 23.2
Mortgage loans, Days delinquent to be considered nonperforming																																								90 days