Retirement Plans - Schedule of Fair Values of Plan Assets (Detail) - USD ($) $ in Millions	Sep. 28, 2018	Sep. 29, 2017
Defined Benefit Plan Disclosure [Line Items]
Plan assets	$ 224.7	$ 215.1
Mutual funds - equities
Defined Benefit Plan Disclosure [Line Items]
Plan assets	29.5	62.6
Mutual funds - debt
Defined Benefit Plan Disclosure [Line Items]
Plan assets	45.2	36.3
Mutual funds - real estate
Defined Benefit Plan Disclosure [Line Items]
Plan assets	9.0	4.9
Other
Defined Benefit Plan Disclosure [Line Items]
Plan assets	23.7	3.2
Insurance contracts
Defined Benefit Plan Disclosure [Line Items]
Plan assets	116.1	107.6
Cash and cash equivalents
Defined Benefit Plan Disclosure [Line Items]
Plan assets	1.2	0.5
Quoted Prices in Active Markets for Identical Instruments (Level 1)
Defined Benefit Plan Disclosure [Line Items]
Plan assets	1.2	0.5
Quoted Prices in Active Markets for Identical Instruments (Level 1) | Mutual funds - equities
Defined Benefit Plan Disclosure [Line Items]
Plan assets	0.0	0.0
Quoted Prices in Active Markets for Identical Instruments (Level 1) | Mutual funds - debt
Defined Benefit Plan Disclosure [Line Items]
Plan assets	0.0	0.0
Quoted Prices in Active Markets for Identical Instruments (Level 1) | Mutual funds - real estate
Defined Benefit Plan Disclosure [Line Items]
Plan assets	0.0	0.0
Quoted Prices in Active Markets for Identical Instruments (Level 1) | Other
Defined Benefit Plan Disclosure [Line Items]
Plan assets	0.0	0.0
Quoted Prices in Active Markets for Identical Instruments (Level 1) | Insurance contracts
Defined Benefit Plan Disclosure [Line Items]
Plan assets	0.0	0.0
Quoted Prices in Active Markets for Identical Instruments (Level 1) | Cash and cash equivalents
Defined Benefit Plan Disclosure [Line Items]
Plan assets	1.2	0.5
Significant Other Observable Inputs (Level 2)
Defined Benefit Plan Disclosure [Line Items]
Plan assets	223.5	214.6
Significant Other Observable Inputs (Level 2) | Mutual funds - equities
Defined Benefit Plan Disclosure [Line Items]
Plan assets	29.5	62.6
Significant Other Observable Inputs (Level 2) | Mutual funds - debt
Defined Benefit Plan Disclosure [Line Items]
Plan assets	45.2	36.3
Significant Other Observable Inputs (Level 2) | Mutual funds - real estate
Defined Benefit Plan Disclosure [Line Items]
Plan assets	9.0	4.9
Significant Other Observable Inputs (Level 2) | Other
Defined Benefit Plan Disclosure [Line Items]
Plan assets	23.7	3.2
Significant Other Observable Inputs (Level 2) | Insurance contracts
Defined Benefit Plan Disclosure [Line Items]
Plan assets	116.1	107.6
Significant Other Observable Inputs (Level 2) | Cash and cash equivalents
Defined Benefit Plan Disclosure [Line Items]
Plan assets	0.0	0.0
Significant Unobservable Inputs (Level 3)
Defined Benefit Plan Disclosure [Line Items]
Plan assets	0.0	0.0
Significant Unobservable Inputs (Level 3) | Mutual funds - equities
Defined Benefit Plan Disclosure [Line Items]
Plan assets	0.0	0.0
Significant Unobservable Inputs (Level 3) | Mutual funds - debt
Defined Benefit Plan Disclosure [Line Items]
Plan assets	0.0	0.0
Significant Unobservable Inputs (Level 3) | Mutual funds - real estate
Defined Benefit Plan Disclosure [Line Items]
Plan assets	0.0	0.0
Significant Unobservable Inputs (Level 3) | Other
Defined Benefit Plan Disclosure [Line Items]
Plan assets	0.0	0.0
Significant Unobservable Inputs (Level 3) | Insurance contracts
Defined Benefit Plan Disclosure [Line Items]
Plan assets	0.0	0.0
Significant Unobservable Inputs (Level 3) | Cash and cash equivalents
Defined Benefit Plan Disclosure [Line Items]
Plan assets	$ 0.0	$ 0.0