Income taxes - reconciliation to effective tax rate (Details)	12 Months Ended
Aug. 31, 2021	Aug. 31, 2020	Aug. 31, 2019
Income Tax Disclosure [Abstract]
Federal statutory rate	21.00%	21.00%	21.00%
State income taxes, net of federal benefit	3.50%	8.80%	0.90%
Foreign income taxed at non-U.S. rates	(4.40%)	(17.00%)	(1.90%)
Non-taxable income	(5.00%)	(47.50%)	(3.60%)
Non-deductible expenses	0.30%	9.00%	0.20%
Tax law changes	17.30%	31.30%	(0.40%)
Change in valuation allowance	(4.70%)	4.10%	2.10%
Tax benefits from restructuring	(4.20%)	0.00%	0.00%
Tax expense on non-operating equity earnings	6.10%	0.00%	0.00%
Uncertain tax positions	6.20%	7.50%	(0.80%)
Goodwill impairment	0.00%	72.50%	0.00%
Tax credits	(1.80%)	(10.30%)	(4.40%)
Other	(0.90%)	(3.40%)	0.10%
Effective income tax rate	33.40%	76.00%	13.20%

Percentage of current income tax expense (benefit) and deferred income tax expense (benefit) pertaining to continuing operations.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 740
-SubTopic 10
-Section 50
-Paragraph 12
-URI http://asc.fasb.org/extlink&oid=121826272&loc=d3e32687-109319

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Percentage of domestic federal statutory tax rate applicable to pretax income (loss).

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Percentage of the difference between reported income tax expense (benefit) and expected income tax expense (benefit) computed by applying the domestic federal statutory income tax rates to pretax income (loss) from continuing operations attributable to changes in the valuation allowance for deferred tax assets.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 740
-SubTopic 10
-Section S99
-Paragraph 1
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Percentage of the difference between reported income tax expense (benefit) and expected income tax expense (benefit) computed by applying the domestic federal statutory income tax rates to pretax income (loss) from continuing operations attributable to equity in earnings (loss) of unconsolidated subsidiaries exempt from income taxes.

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Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
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Percentage of the difference between reported income tax expense (benefit) and expected income tax expense (benefit) computed by applying the domestic federal statutory income tax rates to pretax income (loss) from continuing operations applicable to statutory income tax expense (benefit) outside of the country of domicile.

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Percentage of the difference between reported income tax expense (benefit) and expected income tax expense (benefit) computed by applying the domestic federal statutory income tax rates to pretax income (loss) from continuing operations applicable to state and local income tax expense (benefit), net of federal tax expense (benefit).

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Percentage of the difference between reported income tax expense (benefit) and expected income tax expense (benefit) computed by applying the domestic federal statutory income tax rates to pretax income (loss) from continuing operations attributable to income tax contingencies. Includes, but not limited to, domestic tax contingency, foreign tax contingency, state and local tax contingency, and other contingencies.

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Percentage of the difference between reported income tax expense (benefit) and expected income tax expense (benefit) computed by applying the domestic federal statutory income tax rates to pretax income (loss) from continuing operations attributable to tax credits. Including, but not limited to, research credit, foreign tax credit, investment tax credit, and other tax credits.

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Represents the percentage of change in tax rate due to change in tax law.

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