Investments Mortgages by Year of Origination (Details) (USD $) In Millions, unless otherwise specified	Sep. 30, 2012		Dec. 31, 2011
Investment [Line Items]
Total commercial mortgage loans	$ 2,909.8	[1]	$ 3,138.8	[1]
Year of Origination 2012
Investment [Line Items]
Total commercial mortgage loans	183.7	[1]	0	[1]
Year of Origination 2011
Investment [Line Items]
Total commercial mortgage loans	803.9	[1]	791.2	[1]
Year of Origination 2010
Investment [Line Items]
Total commercial mortgage loans	185.9	[1]	272.1	[1]
Year of Origination 2009
Investment [Line Items]
Total commercial mortgage loans	76.9	[1]	77.8	[1]
Year of Origination 2008
Investment [Line Items]
Total commercial mortgage loans	349.9	[1]	406.5	[1]
Year of Origination 2007
Investment [Line Items]
Total commercial mortgage loans	304.7	[1]	447.7	[1]
Year of Origination 2006 and Prior
Investment [Line Items]
Total commercial mortgage loans	$ 1,004.8	[1]	$ 1,143.5	[1]

[1] Balances do not include allowance for mortgage loan credit losses.