Loans by U.S. Region (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2013		Dec. 31, 2012
Open Option Contracts Written [Line Items]
Loans by property type percentage of total loans	100.00%	[1]	100.00%	[1]
Loans by region percentage of total loans	100.00%	[1]	100.00%	[1]
Total Commercial mortgage loans	$ 3,397.3	[1]	$ 2,874.0	[1]
Pacific
Open Option Contracts Written [Line Items]
Loans by region percentage of total loans	22.30%	[1]	19.60%	[1]
Total Commercial mortgage loans	752.8	[1]	564.1	[1]
South Atlantic
Open Option Contracts Written [Line Items]
Loans by region percentage of total loans	20.80%	[1]	19.50%	[1]
Total Commercial mortgage loans	707.8	[1]	561.0	[1]
Middle Atlantic
Open Option Contracts Written [Line Items]
Loans by region percentage of total loans	12.10%	[1]	11.60%	[1]
Total Commercial mortgage loans	411.4	[1]	332.7	[1]
East North Central
Open Option Contracts Written [Line Items]
Loans by region percentage of total loans	11.30%	[1]	11.80%	[1]
Total Commercial mortgage loans	383.1	[1]	337.8	[1]
West South Central
Open Option Contracts Written [Line Items]
Loans by region percentage of total loans	13.70%	[1]	16.00%	[1]
Total Commercial mortgage loans	467.1	[1]	460.4	[1]
Mountain
Open Option Contracts Written [Line Items]
Loans by region percentage of total loans	7.80%	[1]	7.50%	[1]
Total Commercial mortgage loans	263.9	[1]	214.5	[1]
New England
Open Option Contracts Written [Line Items]
Loans by region percentage of total loans	3.40%	[1]	4.10%	[1]
Total Commercial mortgage loans	116.7	[1]	119.1	[1]
West North Central
Open Option Contracts Written [Line Items]
Loans by region percentage of total loans	6.60%	[1]	7.10%	[1]
Total Commercial mortgage loans	224.9	[1]	205.2	[1]
East South Central
Open Option Contracts Written [Line Items]
Loans by region percentage of total loans	2.00%	[1]	2.80%	[1]
Total Commercial mortgage loans	$ 69.6	[1]	$ 79.2	[1]

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