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Significant Accounting Policies - Changes of Accumulated Other Comprehensive Loss, Net of tax (Details) - USD ($) $ in Millions	12 Months Ended
	Aug. 31, 2019	Aug. 31, 2018	Aug. 31, 2017
Accumulated Other Comprehensive Loss, Net of Tax [Roll Forward]
Beginning balance	$ 1,716.8	$ 1,665.6	$ 1,659.8
Other comprehensive (loss) income before reclassifications	(42.6)	(2.5)
Amounts reclassified from accumulated other comprehensive loss	6.0	(1.5)
Other comprehensive (loss) income items, net of tax	(36.6)	(4.0)	39.7
Reclassification of stranded tax effects of TCJA		0.0
Ending balance	1,918.9	1,716.8	1,665.6
Foreign Currency Items
Accumulated Other Comprehensive Loss, Net of Tax [Roll Forward]
Beginning balance	(53.9)	(28.7)
Other comprehensive (loss) income before reclassifications	(11.5)	(16.5)
Amounts reclassified from accumulated other comprehensive loss	0.0	(8.7)
Other comprehensive (loss) income items, net of tax	(11.5)	(25.2)
Reclassification of stranded tax effects of TCJA		0.0
Ending balance	(65.4)	(53.9)	(28.7)
Defined Benefit Pension Plans
Accumulated Other Comprehensive Loss, Net of Tax [Roll Forward]
Beginning balance	(60.9)	(71.0)
Other comprehensive (loss) income before reclassifications	(31.1)	14.0
Amounts reclassified from accumulated other comprehensive loss	6.0	7.2
Other comprehensive (loss) income items, net of tax	(25.1)	21.2
Reclassification of stranded tax effects of TCJA		(11.1)
Ending balance	(86.0)	(60.9)	(71.0)
Accumulated Other Comprehensive Loss Items
Accumulated Other Comprehensive Loss, Net of Tax [Roll Forward]
Beginning balance	(114.8)	(99.7)	(139.4)
Other comprehensive (loss) income items, net of tax	(36.6)	(4.0)	39.7
Reclassification of stranded tax effects of TCJA		(11.1)
Ending balance	$ (151.4)	$ (114.8)	$ (99.7)

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Amount of increase (decrease) in accumulated other comprehensive income (AOCI) for reclassification to retained earnings of tax effect from remeasurement of deferred tax pursuant to Tax Cuts and Jobs Act.

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Amount after tax, before reclassification adjustments, of other comprehensive income (loss), attributable to parent.

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Amount after tax of other comprehensive income (loss) attributable to parent entity.

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Total of all stockholders' equity (deficit) items, net of receivables from officers, directors, owners, and affiliates of the entity which are attributable to the parent. The amount of the economic entity's stockholders' equity attributable to the parent excludes the amount of stockholders' equity which is allocable to that ownership interest in subsidiary equity which is not attributable to the parent (noncontrolling interest, minority interest). This excludes temporary equity and is sometimes called permanent equity.

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