Fair Value Measurements - Assets and Liabilities Measured at Fair Value on Recurring Basis (Detail) (USD $) In Millions, unless otherwise specified	Sep. 30, 2014	Dec. 31, 2013
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Marketable securities (Other assets)	$ 8.4	$ 8.2
Assets, Fair Value, Total	31.5	14.1
Liabilities, Fair Value, Total	0.2	8.3
Derivative contracts [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative Assets, Fair Value	23.1	5.9
Derivative Liabilities, Fair Value	0.2	8.3
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Marketable securities (Other assets)	8.4	8.2
Assets, Fair Value, Total	8.4	8.2
Liabilities, Fair Value, Total	0
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Derivative contracts [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative Assets, Fair Value	0
Derivative Liabilities, Fair Value	0
Significant Other Observable Inputs (Level 2) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Marketable securities (Other assets)	0
Assets, Fair Value, Total	23.1	5.9
Liabilities, Fair Value, Total	0.2	8.3
Significant Other Observable Inputs (Level 2) [Member] | Derivative contracts [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative Assets, Fair Value	23.1	5.9
Derivative Liabilities, Fair Value	0.2	8.3
Significant Unobservable Inputs (Level 3) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Marketable securities (Other assets)	0
Assets, Fair Value, Total	0
Liabilities, Fair Value, Total	0
Significant Unobservable Inputs (Level 3) [Member] | Derivative contracts [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative Assets, Fair Value	0
Derivative Liabilities, Fair Value	$ 0