Retirement benefits - accumulated benefit obligations in excess of plan assets (Details) - Pension Plan - USD ($) $ in Millions	Aug. 31, 2020	Aug. 31, 2019
Defined Benefit Plan Disclosure [Line Items]
Projected benefit obligation	$ 9,949	$ 8,834
Accumulated benefit obligation	9,937	8,823
Fair value of plan assets	$ 9,614	$ 9,131

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Amount of accumulated benefit obligation for defined benefit plan with accumulated benefit obligation in excess of plan assets.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
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Amount of plan asset for defined benefit plan with accumulated benefit obligation in excess of plan assets.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
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Amount of projected benefit obligation for defined benefit pension plan with accumulated benefit obligation in excess of plan assets.

+ References

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