Fair Value - Assets and Liabilities Measured at Fair Value on Recurring Basis (Detail) - USD ($) $ in Millions	Sep. 27, 2019	Sep. 28, 2018
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Abstract]
Available-for- sale securities	$ 58.8	$ 62.5
Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Abstract]
Derivative assets	2.8
Total assets measured at fair value	61.8	106.6
Contingent consideration	(75.3)	(24.4)
Total liabilities measured at fair value	(75.3)	(24.4)
Fair Value, Measurements, Recurring \| Quoted Prices in Active Markets for Identical Instruments (Level 1)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Abstract]
Derivative assets	0.0
Total assets measured at fair value	0.2	44.1
Contingent consideration	0.0	0.0
Total liabilities measured at fair value	0.0	0.0
Fair Value, Measurements, Recurring \| Significant Other Observable Inputs (Level 2)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Abstract]
Derivative assets	2.8
Total assets measured at fair value	61.6	62.5
Contingent consideration	0.0	0.0
Total liabilities measured at fair value	0.0	0.0
Fair Value, Measurements, Recurring \| Significant Unobservable Inputs (Level 3)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Abstract]
Derivative assets	0.0
Total assets measured at fair value	0.0	0.0
Contingent consideration	(75.3)	(24.4)
Total liabilities measured at fair value	(75.3)	(24.4)
Fair Value, Measurements, Recurring \| MPTC Series B-1 Bonds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Abstract]
Available-for- sale securities	27.1	25.1
Fair Value, Measurements, Recurring \| MPTC Series B-1 Bonds \| Quoted Prices in Active Markets for Identical Instruments (Level 1)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Abstract]
Available-for- sale securities	0.0	0.0
Fair Value, Measurements, Recurring \| MPTC Series B-1 Bonds \| Significant Other Observable Inputs (Level 2)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Abstract]
Available-for- sale securities	27.1	25.1
Fair Value, Measurements, Recurring \| MPTC Series B-1 Bonds \| Significant Unobservable Inputs (Level 3)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Abstract]
Available-for- sale securities	0.0	0.0
Fair Value, Measurements, Recurring \| MPTC Series B-2 Bonds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Abstract]
Available-for- sale securities	25.1	23.1
Fair Value, Measurements, Recurring \| MPTC Series B-2 Bonds \| Quoted Prices in Active Markets for Identical Instruments (Level 1)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Abstract]
Available-for- sale securities	0.0	0.0
Fair Value, Measurements, Recurring \| MPTC Series B-2 Bonds \| Significant Other Observable Inputs (Level 2)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Abstract]
Available-for- sale securities	25.1	23.1
Fair Value, Measurements, Recurring \| MPTC Series B-2 Bonds \| Significant Unobservable Inputs (Level 3)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Abstract]
Available-for- sale securities	0.0	0.0
Fair Value, Measurements, Recurring \| APTC Securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Abstract]
Available-for- sale securities	6.6	6.4
Fair Value, Measurements, Recurring \| APTC Securities \| Quoted Prices in Active Markets for Identical Instruments (Level 1)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Abstract]
Available-for- sale securities	0.0	0.0
Fair Value, Measurements, Recurring \| APTC Securities \| Significant Other Observable Inputs (Level 2)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Abstract]
Available-for- sale securities	6.6	6.4
Fair Value, Measurements, Recurring \| APTC Securities \| Significant Unobservable Inputs (Level 3)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Abstract]
Available-for- sale securities	0.0	0.0
Fair Value, Measurements, Recurring \| GPTC securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Abstract]
Available-for- sale securities		7.9
Fair Value, Measurements, Recurring \| GPTC securities \| Quoted Prices in Active Markets for Identical Instruments (Level 1)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Abstract]
Available-for- sale securities		0.0
Fair Value, Measurements, Recurring \| GPTC securities \| Significant Other Observable Inputs (Level 2)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Abstract]
Available-for- sale securities		7.9
Fair Value, Measurements, Recurring \| GPTC securities \| Significant Unobservable Inputs (Level 3)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Abstract]
Available-for- sale securities		0.0
Money Market Funds \| Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Abstract]
Cash equivalents	0.2	44.1
Money Market Funds \| Fair Value, Measurements, Recurring \| Quoted Prices in Active Markets for Identical Instruments (Level 1)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Abstract]
Cash equivalents	0.2	44.1
Money Market Funds \| Fair Value, Measurements, Recurring \| Significant Other Observable Inputs (Level 2)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Abstract]
Cash equivalents	0.0	0.0
Money Market Funds \| Fair Value, Measurements, Recurring \| Significant Unobservable Inputs (Level 3)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Abstract]
Cash equivalents	$ 0.0	$ 0.0

Fair value portion of probable future economic benefits obtained or controlled by an entity as a result of past transactions or events.

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Amount of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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Amount of short-term, highly liquid investments that are both readily convertible to known amounts of cash and so near their maturity that they present insignificant risk of changes in value because of changes in interest rates. Excludes cash and cash equivalents within disposal group and discontinued operation.

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Fair value, after the effects of master netting arrangements, of a financial asset or other contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset. Includes assets not subject to a master netting arrangement and not elected to be offset.

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Fair value of financial and nonfinancial obligations.

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Contingent Consideration Liability, Fair Value

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