Assets and Liabilities Measured at Fair Value on Recurring Basis (Detail) (USD $) In Millions, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Marketable securities	$ 8.0	$ 13.5
Assets, Fair Value, Total	27.5	62.4
Derivative Liabilities, Fair Value		(1.6)
Liabilities, Fair Value, Total	(8.6)	(1.6)
Hedging contracts [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative Assets, Fair Value	19.5	48.9
Derivative Liabilities, Fair Value	(8.6)
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	8.0	13.5
Assets, Fair Value, Total	8.0	13.5
Derivative Liabilities, Fair Value
Liabilities, Fair Value, Total
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Hedging contracts [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative Assets, Fair Value
Derivative Liabilities, Fair Value
Significant Other Observable Inputs (Level 2) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Marketable securities
Assets, Fair Value, Total	19.5	48.9
Derivative Liabilities, Fair Value		(1.6)
Liabilities, Fair Value, Total	(8.6)	(1.6)
Significant Other Observable Inputs (Level 2) [Member] | Hedging contracts [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative Assets, Fair Value	19.5	48.9
Derivative Liabilities, Fair Value	(8.6)
Significant Unobservable Inputs (Level 3) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Marketable securities
Assets, Fair Value, Total
Derivative Liabilities, Fair Value
Liabilities, Fair Value, Total
Significant Unobservable Inputs (Level 3) [Member] | Hedging contracts [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative Assets, Fair Value
Derivative Liabilities, Fair Value