Stock-based Compensation - Summary of Stock Option Activity (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Millions	12 Months Ended
	Aug. 31, 2020	Aug. 31, 2019	Aug. 31, 2018
Number Outstanding
Balance (in shares)	2,524	3,143	3,366
Exercised (in shares)	(588)	(705)	(622)
Forfeited (in shares)	(122)	(416)	(212)
Balance (in shares)	2,254	2,524	3,143
Vested and exercisable (in shares)	875
Expected to vest (in shares)	1,264
Weighted Average Exercise Price Per Share
Balance (in dollars per share)	$ 168.50	$ 153.05	$ 139.29
Exercised (in dollars per share)	145.54	137.61	113.73
Forfeited (in dollars per share)	218.36	170.54	158.14
Balance (in dollars per share)	189.32	$ 168.50	$ 153.05
Vested and exercisable (in dollars per share)	155.58
Expected to vest (in dollars per share)	$ 209.33
Aggregate Intrinsic Value
Outstanding, aggregate intrinsic value	$ 129.6
Granted – performance-based options	170.4
Expected to vest, aggregate intrinsic value	$ 178.4
Weighted Average Remaining Contractual Life (years)
Outstanding, weighted average remaining contractual term	6 years 7 months 6 days
Vested and exercisable, weighted average remaining contractual life	5 years 1 month 6 days
Expected to vest, weighted average remaining contractual life	7 years 6 months
Non performance-based
Number Outstanding
Granted (in shares)	424	482	575
Weighted Average Exercise Price Per Share
Granted (in dollars per share)	$ 256.43	$ 224.35	$ 190.14
Performance-based
Number Outstanding
Granted (in shares)			17
Weighted Average Exercise Price Per Share
Granted (in dollars per share)			$ 200.20
Non-employee Directors grant
Number Outstanding
Granted (in shares)	16	20	19
Weighted Average Exercise Price Per Share
Granted (in dollars per share)	$ 271.51	$ 207.88	$ 197.75