Schedule of Fair Values of Plan Assets (Detail) (USD $) In Millions, unless otherwise specified	Sep. 26, 2014	Sep. 27, 2013
Defined Benefit Plan Disclosure [Line Items]
Plan assets	$ 188.6	$ 180.8
Mutual Funds Equities
Defined Benefit Plan Disclosure [Line Items]
Plan assets	51.7	49.9
Mutual Funds Debt
Defined Benefit Plan Disclosure [Line Items]
Plan assets	32.5	26.1
Mutual Funds Real Estate
Defined Benefit Plan Disclosure [Line Items]
Plan assets	3.6	3.6
Insurance Contracts
Defined Benefit Plan Disclosure [Line Items]
Plan assets	99.1	86.3
Cash and Cash Equivalents
Defined Benefit Plan Disclosure [Line Items]
Plan assets	1.7	14.9
Quoted Prices in Active Markets for Identical Instruments (Level 1)
Defined Benefit Plan Disclosure [Line Items]
Plan assets	1.7	14.9
Quoted Prices in Active Markets for Identical Instruments (Level 1) | Cash and Cash Equivalents
Defined Benefit Plan Disclosure [Line Items]
Plan assets	1.7	14.9
Significant Other Observable Inputs (Level 2)
Defined Benefit Plan Disclosure [Line Items]
Plan assets	186.9	165.9
Significant Other Observable Inputs (Level 2) | Mutual Funds Equities
Defined Benefit Plan Disclosure [Line Items]
Plan assets	51.7	49.9
Significant Other Observable Inputs (Level 2) | Mutual Funds Debt
Defined Benefit Plan Disclosure [Line Items]
Plan assets	32.5	26.1
Significant Other Observable Inputs (Level 2) | Mutual Funds Real Estate
Defined Benefit Plan Disclosure [Line Items]
Plan assets	3.6	3.6
Significant Other Observable Inputs (Level 2) | Insurance Contracts
Defined Benefit Plan Disclosure [Line Items]
Plan assets	$ 99.1	$ 86.3