Mortgage Loans by Property Type (Detail) (USD $) In Millions, unless otherwise specified	Dec. 31, 2013		Dec. 31, 2012
Mortgage Loans on Real Estate [Line Items]
Mortgage Loans	$ 1,815.1	[1]	$ 1,712.7
Percent of Total	100.00%		100.00%
Apartment
Mortgage Loans on Real Estate [Line Items]
Mortgage Loans	61.1		47.2
Percent of Total	3.30%		2.70%
Industrial
Mortgage Loans on Real Estate [Line Items]
Mortgage Loans	567.8		545.7
Percent of Total	31.30%		31.90%
Office
Mortgage Loans on Real Estate [Line Items]
Mortgage Loans	776.5		721.2
Percent of Total	42.80%		42.10%
Retail
Mortgage Loans on Real Estate [Line Items]
Mortgage Loans	$ 409.7		$ 398.6
Percent of Total	22.60%		23.30%

[1] (1)The amortized cost for fixed maturity securities and mortgage loans represents original cost reduced by repayments, write-downs from other-than-temporary declines in fair value, amortization of premiums, and/or accretion of discounts.