Location of and Gain (Loss) on Derivative Financial Instruments Not Designated as Hedging Instruments (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Net Realized Investment Gain (Loss)
Gain (Loss) on Embedded Derivative	$ 30.7	$ 51.8	$ (39.4)
Net Realized Investments Gain (Loss)
Net Realized Investment Gain (Loss)
Credit Default Swap Loss	(1.9)	0	0
Gain (Loss) on Embedded Derivative	30.7	51.8	(39.4)
Gains (Losses) on Derivatives Not Designated as Hedging Instruments	$ 28.8	$ 51.8	$ (39.4)