Derivative Instruments and Hedging Activities - Location and Fair Value Amounts of Derivative Instruments Reported in Balance Sheet (Detail) - Designated as Hedging Instrument - Commodity contracts - USD ($) $ in Millions	Mar. 31, 2016	Dec. 31, 2015
Asset Derivatives
Fair Value of Derivative Instruments, Assets	$ 30.2	$ 38.6
Liability Derivatives
Fair Value of Derivative Instruments, Liabilities	0.0	0.0
Current assets: Fair value of derivative contracts
Asset Derivatives
Fair Value of Derivative Instruments, Assets	30.2	38.6
Long-term assets: Fair value of derivative contracts
Asset Derivatives
Fair Value of Derivative Instruments, Assets	0.0	0.0
Current liabilities: Fair value of derivative contracts
Liability Derivatives
Fair Value of Derivative Instruments, Liabilities	0.0	0.0
Long-term liabilities: Fair value of derivative contracts
Liability Derivatives
Fair Value of Derivative Instruments, Liabilities	$ 0.0	$ 0.0