Retirement Plans - Schedule of Fair Values of Plan Assets (Detail) - USD ($) $ in Millions	Sep. 27, 2019	Sep. 28, 2018
Defined Benefit Plan Disclosure [Line Items]
Plan assets	$ 254.2	$ 224.7
Mutual funds - equities
Defined Benefit Plan Disclosure [Line Items]
Plan assets	51.9	29.5
Mutual funds - debt
Defined Benefit Plan Disclosure [Line Items]
Plan assets	112.5	45.2
Hedge funds
Defined Benefit Plan Disclosure [Line Items]
Plan assets	4.0
Mutual funds - real estate
Defined Benefit Plan Disclosure [Line Items]
Plan assets	43.9	9.0
Other
Defined Benefit Plan Disclosure [Line Items]
Plan assets	27.1	23.7
Insurance contracts
Defined Benefit Plan Disclosure [Line Items]
Plan assets	13.0	116.1
Cash and cash equivalents
Defined Benefit Plan Disclosure [Line Items]
Plan assets	1.8	1.2
Quoted Prices in Active Markets for Identical Instruments (Level 1)
Defined Benefit Plan Disclosure [Line Items]
Plan assets	1.8	1.2
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) | Hedge funds
Defined Benefit Plan Disclosure [Line Items]
Plan assets	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	1.8	1.2
Significant Other Observable Inputs (Level 2)
Defined Benefit Plan Disclosure [Line Items]
Plan assets	252.4	223.5
Significant Other Observable Inputs (Level 2) | Mutual funds - equities
Defined Benefit Plan Disclosure [Line Items]
Plan assets	51.9	29.5
Significant Other Observable Inputs (Level 2) | Mutual funds - debt
Defined Benefit Plan Disclosure [Line Items]
Plan assets	112.5	45.2
Significant Other Observable Inputs (Level 2) | Hedge funds
Defined Benefit Plan Disclosure [Line Items]
Plan assets	4.0
Significant Other Observable Inputs (Level 2) | Mutual funds - real estate
Defined Benefit Plan Disclosure [Line Items]
Plan assets	43.9	9.0
Significant Other Observable Inputs (Level 2) | Other
Defined Benefit Plan Disclosure [Line Items]
Plan assets	27.1	23.7
Significant Other Observable Inputs (Level 2) | Insurance contracts
Defined Benefit Plan Disclosure [Line Items]
Plan assets	13.0	116.1
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) | Hedge funds
Defined Benefit Plan Disclosure [Line Items]
Plan assets	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