Financial Instruments Carried at Fair Value on Recurring Basis (Detail) - USD ($) $ in Millions	Sep. 30, 2016	Dec. 31, 2015
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Derivative Contracts	$ 31.9	$ 12.6
Money market funds	38.9	188.3
Fixed maturity and open ended mutual funds	32.9	31.9
Total, Assets	103.7	232.8
Derivatives, Liabilities	30.6	10.4
Total, Liabilities	30.6	10.4
Fair Value Inputs Level 1 [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Money market funds	38.9	188.3
Fixed maturity and open ended mutual funds	32.9	31.9
Total, Assets	71.8	220.2
Fair Value Inputs Level 2 [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Derivative Contracts	31.9	12.6
Total, Assets	31.9	12.6
Derivatives, Liabilities	30.6	10.4
Total, Liabilities	$ 30.6	$ 10.4