Net Fair Value of Commodity Price Risk (Detail) (USD $) In Millions, unless otherwise specified	Apr. 20, 2013
Derivatives, Fair Value [Line Items]
Assets	$ 1.1
Liabilities	(7.9)
Net Fair Value	(6.8)
Other Current Assets
Derivatives, Fair Value [Line Items]
Assets	1.0
Other Long Term Assets
Derivatives, Fair Value [Line Items]
Assets	0.1
Other Current Liabilities
Derivatives, Fair Value [Line Items]
Liabilities	(7.9)
Level 1
Derivatives, Fair Value [Line Items]
Liabilities	(7.9)
Net Fair Value	(7.9)
Level 1 | Other Current Liabilities
Derivatives, Fair Value [Line Items]
Liabilities	(7.9)
Level 2
Derivatives, Fair Value [Line Items]
Assets	1.1
Net Fair Value	1.1
Level 2 | Other Current Assets
Derivatives, Fair Value [Line Items]
Assets	1.0
Level 2 | Other Long Term Assets
Derivatives, Fair Value [Line Items]
Assets	$ 0.1