Significant Accounting Policies - Components of Other Comprehensive Income Loss (Details) - USD ($) $ in Millions	12 Months Ended
	Aug. 31, 2018	Aug. 31, 2017	Aug. 31, 2016
Foreign currency translation adjustments - Before Tax Amount
Foreign currency translation adjustments	$ (25.2)	$ 19.0	$ (5.6)
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	(25.2)	19.0	(5.6)
Defined benefit pension plans - Before Tax Amounts
Actuarial gains (losses)	18.4	18.3	(42.2)
Amortization of Defined benefit pension items - Prior service cost	3.1	3.1	3.1
Amortization of Defined benefit pension items - Actuarial losses	6.8	8.9	4.9
Total defined benefit plans, net - before tax	28.3	30.3	(34.2)
Defined benefit pension plans - Tax (Expense) or Benefit
Actuarial gains (losses)	4.4	5.7	(13.5)
Amortization of Defined benefit pension items - Prior service cost	0.7	0.7	1.1
Amortization of Defined benefit pension items - Actuarial losses	(2.0)	(3.2)	(1.6)
Total defined benefit plans, net - tax	(7.1)	(9.6)	10.8
Defined benefit pension plans - Net of Tax Amount
Actuarial gains (losses)	14.0	12.6	(28.7)
Amortization of Defined benefit pension items - Prior service cost	2.4	2.4	2.0
Amortization of Defined benefit pension items - Actuarial losses	4.8	5.7	3.3
Total defined benefit plans, net - net of tax	21.2	20.7	(23.4)
Other comprehensive income (loss) before tax	3.1	49.3	(39.8)
Other comprehensive income (loss), tax	7.1	9.6	(10.8)
Other comprehensive income (loss) items, net of tax	$ 4.0	$ (39.7)	$ 29.0