Special Charge (Details) - USD ($) $ in Millions	3 Months Ended
	Nov. 30, 2017	Nov. 30, 2016
Restructuring Cost and Reserve [Line Items]
Total special charges	$ 0.2	$ 1.2
Restructuring Reserve [Roll Forward]
Balance, beginning of period	12.6
Severance costs	0.2
Payments made during the period	(2.6)
Balance, end of period	10.2
Restructuring Charges
Restructuring Cost and Reserve [Line Items]
Total special charges	0.2	1.2
Restructuring Charges | Severance and employee-related costs
Restructuring Cost and Reserve [Line Items]
Total special charges	0.2	(0.2)
Restructuring Charges | Lease termination and other costs
Restructuring Cost and Reserve [Line Items]
Total special charges	0.0	$ 1.4
Fiscal 2017 Actions
Restructuring Reserve [Roll Forward]
Balance, beginning of period	11.2
Severance costs	0.2
Payments made during the period	(2.1)
Balance, end of period	9.3
Fiscal 2016 Actions
Restructuring Reserve [Roll Forward]
Balance, beginning of period	1.4
Severance costs	0.0
Payments made during the period	(0.5)
Balance, end of period	$ 0.9