Investments - Mortgages by Year of Origination (Details) (USD $) In Millions, unless otherwise specified	Sep. 30, 2014		Dec. 31, 2013
Investment [Line Items]
Loans Receivable, Gross, Commercial, Real Estate	$ 3,565.9	[1]	$ 3,397.3	[1]
Year of Origination 2014
Investment [Line Items]
Loans Receivable, Gross, Commercial, Real Estate	445.8	[1]	0	[1]
Year of Origination 2013
Investment [Line Items]
Loans Receivable, Gross, Commercial, Real Estate	767.1	[1]	785.2	[1]
Year of Origination 2012
Investment [Line Items]
Loans Receivable, Gross, Commercial, Real Estate	889.2	[1]	908.1	[1]
Year of Origination 2011
Investment [Line Items]
Loans Receivable, Gross, Commercial, Real Estate	717.4	[1]	792.8	[1]
Year of Origination 2010
Investment [Line Items]
Loans Receivable, Gross, Commercial, Real Estate	108.6	[1]	121.1	[1]
Year of Origination 2009
Investment [Line Items]
Loans Receivable, Gross, Commercial, Real Estate	39.1	[1]	68.4	[1]
Year Of Origination 2008 And Prior [Member]
Investment [Line Items]
Loans Receivable, Gross, Commercial, Real Estate	$ 598.7	[1]	$ 721.7	[1]

[1] Balances do not include collective valuation allowance for losses.