Supplemental information - Summary of Dividends per Share (Details) - $ / shares	3 Months Ended						9 Months Ended
	May 31, 2021	Feb. 28, 2021	Nov. 30, 2020	May 31, 2020	Feb. 29, 2020	Nov. 30, 2019	May 31, 2021	May 31, 2020
Cash and Cash Equivalents [Abstract]
Cash dividends declared (in dollars per share)	$ 0.4675	$ 0.4675	$ 0.4675	$ 0.4575	$ 0.4575	$ 0.4575	$ 1.4025	$ 1.3725