Unaudited Quarterly Results - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended		12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2014	Dec. 31, 2013
Interim Period, Costs Not Allocable
Reserve Increase for Long-term Care	$ 698.2		$ 698.2
Reserve Charge for Long-term Care Product, After Tax	453.8
Unclaimed Death Benefit Reserve Increase Before Taxes		95.5		95.5
Unclaimed Death Benefit Reserve Increase After Tax		62.1
Waiver of Premium Benefit Reserve Decrease Before Tax		85.0
Waiver of Premium Benefit Reserve Decrease After Tax		55.2
Pension Settlement Loss
Interim Period, Costs Not Allocable
Non-operating Retirement-related Loss	64.4
Non-operating Retirement Related Loss, After Tax	$ 41.9