Borrowings and Credit Arrangements - Interest Expense Senior Notes (Details) - Senior Notes - USD ($) $ in Millions	12 Months Ended
	Sep. 26, 2020	Sep. 28, 2019	Sep. 29, 2018
Debt Instrument [Line Items]
Interest expense	$ 62.7	$ 62.7	$ 69.2
Non-cash interest expense	2.8	2.8	3.6
2028 Senior Notes
Debt Instrument [Line Items]
Interest expense	19.2	19.2	13.3
Non-cash interest expense	$ 0.7	0.7	0.5
Interest rate (percent)	4.625%
2025 Senior Notes
Debt Instrument [Line Items]
Interest expense	$ 43.5	43.5	34.7
Non-cash interest expense	$ 2.1	2.1	1.6
Interest rate (percent)	4.375%
2022 Senior Notes
Debt Instrument [Line Items]
Interest expense	$ 0.0	0.0	21.2
Non-cash interest expense	$ 0.0	$ 0.0	$ 1.5
Interest rate (percent)		5.25%