Gains and Losses on Derivatives Not Designated as Hedging Instruments (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
Derivative Instruments, Gain (Loss)
Gain (Loss) on Derivatives	$ (2.5)	$ (1.1)
Not Designated as Hedging Instrument
Derivative Instruments, Gain (Loss)
Gain (Loss) on Derivatives	(6.9)	(5.0)
Not Designated as Hedging Instrument | Credit Default Swaps
Derivative Instruments, Gain (Loss)
Gain (Loss) on Derivatives	0.0	(0.3)
Not Designated as Hedging Instrument | Foreign Exchange Contracts
Derivative Instruments, Gain (Loss)
Gain (Loss) on Derivatives	(1.3)	(0.8)
Not Designated as Hedging Instrument | Embedded Derivative in Modified Coinsurance Arrangement
Derivative Instruments, Gain (Loss)
Gain (Loss) on Derivatives	$ (5.6)	$ (3.9)