Financial Instruments Carried at Fair Value on Recurring Basis (Detail) - USD ($) $ in Millions	Jun. 30, 2016	Dec. 31, 2015
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Derivative Contracts	$ 39.0	$ 12.6
Money market funds	55.5	188.3
Fixed maturity and open ended mutual funds	32.9	31.9
Total, Assets	127.4	232.8
Derivatives, Liabilities	37.0	10.4
Total, Liabilities	37.0	10.4
Fair Value Inputs Level 1 [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Money market funds	55.5	188.3
Fixed maturity and open ended mutual funds	32.9	31.9
Total, Assets	88.4	220.2
Fair Value Inputs Level 2 [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Derivative Contracts	39.0	12.6
Total, Assets	39.0	12.6
Derivatives, Liabilities	37.0	10.4
Total, Liabilities	$ 37.0	$ 10.4