Assets and Liabilities Measured at Fair Value on Recurring Basis (Detail) (USD $) In Millions, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Marketable securities	$ 13.9	$ 13.5
Assets, Fair Value, Total	39.4	62.4
Liabilities, Fair Value, Total	(8.4)	(1.6)
Hedging contracts
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative Assets, Fair Value	25.5	48.9
Derivative Liabilities, Fair Value	(8.4)	(1.6)
Quoted Prices in Active Markets for Identical Assets (Level 1)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Marketable securities	13.9	13.5
Assets, Fair Value, Total	13.9	13.5
Significant Other Observable Inputs (Level 2)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, Fair Value, Total	25.5	48.9
Liabilities, Fair Value, Total	(8.4)	(1.6)
Significant Other Observable Inputs (Level 2) | Hedging contracts
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative Assets, Fair Value	25.5	48.9
Derivative Liabilities, Fair Value	$ (8.4)	$ (1.6)