Derivative Instruments and Hedging Activities - Gains or Losses Related to Changes in Fair Value and Cash Settlements on Derivatives Not Qualifying as Hedging Instruments (Detail) (Commodity Contracts [Member], USD $) In Millions, unless otherwise specified	3 Months Ended	6 Months Ended
	Jun. 30, 2014	Jun. 30, 2014
Commodity Contracts [Member]
Derivatives, Fair Value [Line Items]
Cash settlements on Derivative Instruments not Qualifying Hedges	$ 0	$ 0
Change in fair value on Derivative Instruments not Qualifying Hedges	(1.5)	(1.5)
Total losses on Derivative Instruments not Qualifying Hedges	$ (1.5)	$ (1.5)