Assets And Liabilities Measured And Recorded At Fair Value On Recurring Basis (Detail) (Fair Value, Measurements, Recurring, USD $) In Millions, unless otherwise specified	Jun. 30, 2013	Dec. 31, 2012
Commercial Paper | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	$ 35.3	$ 28.3
Commercial Paper | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents
Commercial Paper | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents
Common stock - available-for-sale investment | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Prepaid and other current assets	22.1	20.7
Common stock - available-for-sale investment | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Prepaid and other current assets
Common stock - available-for-sale investment | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Prepaid and other current assets
Commodity Contract | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Mark-to-market liability derivatives
Commodity Contract | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Mark-to-market liability derivatives	0.5
Mark-to-market Asset derivatives		0.2
Commodity Contract | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Mark-to-market liability derivatives