Other Balance Sheet Information - Property, Plant and Equipment (Detail) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
Dec. 25, 2021	Dec. 26, 2020	Sep. 26, 2020	Sep. 25, 2021
Balance Sheet Related Disclosures [Abstract]
Equipment	$ 463.5			$ 467.1
Equipment under customer usage agreements	492.1			484.6
Building and improvements	192.5			191.2
Leasehold improvements	51.0			49.7
Land	41.3			41.3
Furniture and fixtures	17.1			16.8
Finance Lease, Right-of-Use Asset, after Accumulated Amortization	8.8			9.9
Property, plant and equipment, gross	1,266.3			1,260.6
Less – accumulated depreciation and amortization	(712.0)			(695.9)
Property, plant and equipment, net	554.3			564.7
Grants received from Department of defense		$ 119.3	$ 7.6
Grants Receivable, Current	81.4
Department of defense funds received	$ 21.3			$ 21.1

Department of defense funds received

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Gross amount at the balance sheet date of long-lived, depreciable asset that are equipment placed at customer locations for which title is not transferred to the Company's customers.

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Grants received from Department of defense

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Gross amount as of the balance sheet date of long-lived, depreciable assets that include manufacturing and other equipment with finite lives used to produce goods and services, and computer equipment and software.

+ References

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Amount of accumulated depreciation, depletion and amortization for physical assets used in the normal conduct of business to produce goods and services.

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Amount before accumulated depreciation of building structures held for productive use including addition, improvement, or renovation to the structure, including, but not limited to, interior masonry, interior flooring, electrical, and plumbing.

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Amount, after accumulated amortization, of right-of-use asset from finance lease.

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Amount before accumulated depreciation of equipment commonly used in offices and stores that have no permanent connection to the structure of a building or utilities. Examples include, but are not limited to, desks, chairs, tables, and bookcases.

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Carrying amount as of the balance sheet date of amounts due under the terms of governmental, corporate, or foundation grants. For classified balance sheets, represents the current amount receivable, that is amounts expected to be collected within one year or the normal operating cycle, if longer.

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Amount before accumulated depletion of real estate held for productive use, excluding land held for sale.

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Amount before accumulated depreciation of additions or improvements to assets held under a lease arrangement.

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Amount before accumulated depreciation, depletion and amortization of physical assets used in the normal conduct of business and not intended for resale. Examples include, but are not limited to, land, buildings, machinery and equipment, office equipment, and furniture and fixtures.

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Amount after accumulated depreciation, depletion and amortization of physical assets used in the normal conduct of business to produce goods and services and not intended for resale. Examples include, but are not limited to, land, buildings, machinery and equipment, office equipment, and furniture and fixtures.

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