Investments - Loans by Property Type (Details) (USD $) In Millions, unless otherwise specified	Mar. 31, 2014		Dec. 31, 2013
Investment Holdings [Line Items]
Loans by property type percentage of total loans	100.00%	[1]	100.00%	[1]
Loans Receivable, Gross, Commercial, Real Estate	$ 3,378.2	[1]	$ 3,397.3	[1]
Industrial
Investment Holdings [Line Items]
Loans by property type percentage of total loans	28.60%	[1]	28.60%	[1]
Loans Receivable, Gross, Commercial, Real Estate	966.1	[1]	972.6	[1]
Retail
Investment Holdings [Line Items]
Loans by property type percentage of total loans	32.10%	[1]	31.90%	[1]
Loans Receivable, Gross, Commercial, Real Estate	1,084.2	[1]	1,082.1	[1]
Office
Investment Holdings [Line Items]
Loans by property type percentage of total loans	12.30%	[1]	13.60%	[1]
Loans Receivable, Gross, Commercial, Real Estate	416.9	[1]	462.1	[1]
Apartments
Investment Holdings [Line Items]
Loans by property type percentage of total loans	13.50%	[1]	13.10%	[1]
Loans Receivable, Gross, Commercial, Real Estate	458.1	[1]	445.2	[1]
Hotel/Motel
Investment Holdings [Line Items]
Loans by property type percentage of total loans	4.40%	[1]	5.40%	[1]
Loans Receivable, Gross, Commercial, Real Estate	147.5	[1]	182.8	[1]
Mixed Use
Investment Holdings [Line Items]
Loans by property type percentage of total loans	4.00%	[1]	2.10%	[1]
Loans Receivable, Gross, Commercial, Real Estate	133.8	[1]	70.9	[1]
Other
Investment Holdings [Line Items]
Loans by property type percentage of total loans	5.10%	[1]	5.30%	[1]
Loans Receivable, Gross, Commercial, Real Estate	$ 171.6	[1]	$ 181.6	[1]

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