Significant Accounting Policies - Components of Other Comprehensive Income Loss (Details) - USD ($) $ in Millions	12 Months Ended
	Aug. 31, 2021	Aug. 31, 2020	Aug. 31, 2019
Foreign currency translation adjustments - Net of Tax Amount
Foreign currency translation adjustments	$ 13.3	$ 11.9	$ (11.5)
Defined benefit pension plans - Net of Tax Amount
Tax adjustments, after tax	27.2	11.3
Total defined benefit plans, net - net of tax	21.2	6.8	(25.1)
Other comprehensive income (loss) before tax	43.1	20.8	(44.3)
Other comprehensive income (loss), tax	(8.6)	(2.1)	7.7
Other comprehensive income (loss) items, net of tax	34.5	18.7	(36.6)
Foreign Currency Items
Foreign currency translation adjustments - Before Tax Amount
Foreign currency translation adjustments	13.3	11.9	(11.5)
Foreign currency translation adjustments - Tax (Expense) or Benefit
Foreign currency translation adjustments	0.0	0.0	0.0
Foreign currency translation adjustments - Net of Tax Amount
Foreign currency translation adjustments	13.3	11.9	(11.5)
Defined benefit pension plans - Net of Tax Amount
Tax adjustments, after tax	13.3	11.9
Other comprehensive income (loss) items, net of tax	13.3	11.9
Tax adjustments
Defined benefit pension plans - Before Tax Amounts
Tax adjustments, before tax	0.0	0.0	0.0
Defined benefit pension plans - Tax (Expense) or Benefit
Tax adjustments	(3.2)	0.0	0.0
Defined benefit pension plans - Net of Tax Amount
Tax adjustments, after tax	(3.2)	0.0	0.0
Actuarial gains (losses)
Defined benefit pension plans - Before Tax Amounts
Actuarial gains (losses)	17.5	(0.7)	(40.8)
Defined benefit pension plans - Tax (Expense) or Benefit
Actuarial gains (losses)	(3.6)	0.1	9.7
Defined benefit pension plans - Net of Tax Amount
Actuarial gains (losses)	13.9	(0.6)	(31.1)
Prior service cost
Defined benefit pension plans - Before Tax Amounts
Amortization of Defined benefit pension items - Prior service cost	2.9	4.0	3.5
Defined benefit pension plans - Tax (Expense) or Benefit
Amortization of Defined benefit pension items - Prior service cost	(0.6)	(0.9)	(0.9)
Defined benefit pension plans - Net of Tax Amount
Amortization of Defined benefit pension items - Prior service cost	2.3	3.1	2.6
Actuarial losses
Defined benefit pension plans - Before Tax Amounts
Amortization of Defined benefit pension items - Actuarial losses	5.5	5.6	4.1
Defined benefit pension plans - Tax (Expense) or Benefit
Amortization of Defined benefit pension items - Actuarial losses	(1.2)	(1.3)	(1.0)
Defined benefit pension plans - Net of Tax Amount
Amortization of Defined benefit pension items - Actuarial losses	4.3	4.3	3.1
Settlement losses
Defined benefit pension plans - Before Tax Amounts
Amortization of Defined benefit pension items - Settlement losses	3.9	0.0	0.4
Defined benefit pension plans - Tax (Expense) or Benefit
Amortization of Defined benefit pension items - Settlement losses	0.0	0.0	(0.1)
Defined benefit pension plans - Net of Tax Amount
Amortization of Defined benefit pension items - Settlement losses	3.9	0.0	0.3
Defined Benefit Pension Plans
Defined benefit pension plans - Before Tax Amounts
Total defined benefit plans, net - before tax	29.8	8.9	(32.8)
Defined benefit pension plans - Tax (Expense) or Benefit
Total defined benefit plans, net - tax	(8.6)	(2.1)	7.7
Defined benefit pension plans - Net of Tax Amount
Tax adjustments, after tax	13.9	(0.6)
Total defined benefit plans, net - net of tax	21.2	6.8	$ (25.1)
Other comprehensive income (loss) items, net of tax	$ 21.2	$ 6.8