Investments - Loans by Property Type (Details) (USD $) In Millions, unless otherwise specified	Jun. 30, 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	$ 3,435.6	[1]	$ 3,397.3	[1]
Industrial
Investment Holdings [Line Items]
Loans by property type percentage of total loans	27.10%	[1]	28.60%	[1]
Loans Receivable, Gross, Commercial, Real Estate	931.4	[1]	972.6	[1]
Retail
Investment Holdings [Line Items]
Loans by property type percentage of total loans	31.40%	[1]	31.90%	[1]
Loans Receivable, Gross, Commercial, Real Estate	1,080.3	[1]	1,082.1	[1]
Office
Investment Holdings [Line Items]
Loans by property type percentage of total loans	12.90%	[1]	13.60%	[1]
Loans Receivable, Gross, Commercial, Real Estate	444.0	[1]	462.1	[1]
Apartments
Investment Holdings [Line Items]
Loans by property type percentage of total loans	14.20%	[1]	13.10%	[1]
Loans Receivable, Gross, Commercial, Real Estate	486.3	[1]	445.2	[1]
Hotel/Motel
Investment Holdings [Line Items]
Loans by property type percentage of total loans	4.60%	[1]	5.40%	[1]
Loans Receivable, Gross, Commercial, Real Estate	158.1	[1]	182.8	[1]
Mixed Use
Investment Holdings [Line Items]
Loans by property type percentage of total loans	4.20%	[1]	2.10%	[1]
Loans Receivable, Gross, Commercial, Real Estate	143.9	[1]	70.9	[1]
Other
Investment Holdings [Line Items]
Loans by property type percentage of total loans	5.60%	[1]	5.30%	[1]
Loans Receivable, Gross, Commercial, Real Estate	$ 191.6	[1]	$ 181.6	[1]

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