Employee Benefit Plans - Narrative (Details) - USD ($) $ in Millions	12 Months Ended
	Aug. 28, 2021	Aug. 29, 2020	Aug. 31, 2019
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Contributions charged to expense under the plan	$ 19.9	$ 16.6	$ 19.7
SERP
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Amounts charged to expense related to the plan	2.9	2.6	2.1
Accumulated benefit obligations	30.6	30.7
UniFirst Plan
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Amounts charged to expense related to the plan	$ 0.2	0.2	0.3
Minimum annual interest rate	3.25%
Textilease Plan
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Amounts charged to expense related to the plan	$ 0.0	0.0	$ 0.5
Minimum annual interest rate	1.50%
Pension Plans
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Accumulated benefit obligations	$ 5.0	$ 5.5