Investments - Mortgages by Year of Origination (Details) (USD $) In Millions, unless otherwise specified	Mar. 31, 2014		Dec. 31, 2013
Investment [Line Items]
Loans Receivable, Gross, Commercial, Real Estate	$ 3,378.2	[1]	$ 3,397.3	[1]
Year of Origination 2014
Investment [Line Items]
Loans Receivable, Gross, Commercial, Real Estate	72.4	[1]	0	[1]
Year of Origination 2013
Investment [Line Items]
Loans Receivable, Gross, Commercial, Real Estate	780.5	[1]	785.2	[1]
Year of Origination 2012
Investment [Line Items]
Loans Receivable, Gross, Commercial, Real Estate	903.2	[1]	908.1	[1]
Year of Origination 2011
Investment [Line Items]
Loans Receivable, Gross, Commercial, Real Estate	780.0	[1]	792.8	[1]
Year of Origination 2010
Investment [Line Items]
Loans Receivable, Gross, Commercial, Real Estate	116.8	[1]	121.1	[1]
Year of Origination 2009
Investment [Line Items]
Loans Receivable, Gross, Commercial, Real Estate	68.1	[1]	68.4	[1]
Year Of Origination 2008 And Prior [Member]
Investment [Line Items]
Loans Receivable, Gross, Commercial, Real Estate	$ 657.2	[1]	$ 721.7	[1]

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