Location of and Gain (Loss) on Derivative Financial Instruments Not Designated as Hedging Instruments (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013
Net Realized Investment Gain (Loss)
Loss on Credit Default Swaps	$ (0.4)	$ (0.2)	$ (0.8)	$ (0.5)
Gain on Embedded Derivative	12.4	12.4	20.9	18.8
Gains (Losses) on Derivatives Not Designated as Hedging Instruments	$ 12.0	$ 12.2	$ 20.1	$ 18.3