Derivative Instruments and Hedging Activities - Location and Fair Value Amounts of Derivative Instruments Not Qualifying as Hedging Instruments Reported in Balance Sheet (Detail) - USD ($) $ in Millions	Jun. 30, 2015	Dec. 31, 2014
Commodity Contracts [Member] | Current Assets [Member]
Asset Derivatives
Fair Value of Derivative Instruments	$ 6.8	$ 12.1