Summary of Significant Accounting Policies (Details) $ in Millions	3 Months Ended		6 Months Ended
	Mar. 28, 2021 USD ($) store	Mar. 29, 2020 USD ($)	Mar. 28, 2021 USD ($) store	Sep. 28, 2020 USD ($)	Sep. 27, 2020 USD ($)
Payroll Tax Incentives	$ 97.4	$ 35.0	$ 117.2
Government subsidies receivables	158.6		158.6		$ 155.1
Deferred Payroll Tax Payments	5.2		81.7
Deferred Payroll Tax Payments, Current	116.4		116.4
Deferred Payroll Tax Payments, Noncurrent	$ 116.4		$ 116.4
Identified Store Closures | store	760		760
Restructuring and Related Cost, Incurred Cost	$ 23.0		$ 95.2
Operating Lease, Liability	8,874.1		8,874.1
Accrued payroll and benefits	646.1		646.1		696.0
Payments for Restructuring			23.2
Retained Earnings (Accumulated Deficit)	(8,124.3)		$ (8,124.3)		$ (7,815.6)
Accounting Standards Update 2016-13 [Member]
Retained Earnings (Accumulated Deficit)				$ 2.2
Minimum [Member]
Timing of Store Closures			9
Restructuring and Related Cost, Expected Cost	30.0		$ 30.0
Maximum [Member]
Timing of Store Closures			12
Restructuring and Related Cost, Expected Cost	40.0		$ 40.0
Facility Closing [Member]
Restructuring and Related Cost, Incurred Cost	8.6		51.2
Lease termination [Member]
Restructuring and Related Cost, Incurred Cost	14.4		44.0
Operating Lease, Liability	21.4		21.4
Employee Severance [Member]
Accrued payroll and benefits	$ 10.4		$ 10.4
US and Canada [Member]
Number of Store Closures | store			800