Stock-based Compensation - Summary of Weighted Average Assumptions (Details) - $ / shares	12 Months Ended
Aug. 31, 2020	Aug. 31, 2019	Aug. 31, 2018
Stock options \| Employee
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Dividend yield	1.09%	1.15%	1.32%
Weighted average estimated fair value (in dollars per share)	$ 60.33	$ 57.12	$ 48.39
Weighted average exercise price (in dollars per share)	$ 256.43	$ 224.35	$ 190.42
Fair value as a percentage of exercise price	23.50%	25.50%	25.40%
Stock options \| Director Plan \| Non-employee directors
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Term structure of risk-free interest rate	164.00%	2.51%	2.34%
Expected life	5 years 4 months 24 days	5 years 4 months 24 days	5 years 4 months 24 days
Term structure of volatility	22.00%	20.50%	19.70%
Dividend yield	111.00%	1.17%	1.16%
Weighted average estimated fair value (in dollars per share)	$ 54.74	$ 42.77	$ 38.76
ESPP
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Term structure of risk-free interest rate	0.95%	2.33%	1.55%
Expected life	3 months	3 months	3 months
Term structure of volatility	20.04%	10.89%	10.19%
Dividend yield	1.08%	1.12%	1.27%
Weighted average estimated fair value (in dollars per share)	$ 50.69	$ 41.06	$ 31.83
Weighted average exercise price (in dollars per share)	$ 234.41	$ 205.64	$ 160.34
Minimum \| Stock options \| Employee
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Term structure of risk-free interest rate	0.10%	1.28%	1.28%
Expected life	7 years 2 months 12 days	7 years 1 month 6 days	7 years 4 months 24 days
Term structure of volatility	25.00%	18.00%	19.00%
Maximum \| Stock options \| Employee
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Term structure of risk-free interest rate	1.79%	3.14%	2.41%
Expected life	7 years 2 months 12 days	7 years 1 month 6 days	7 years 4 months 24 days
Term structure of volatility	25.00%	29.00%	29.00%

Discount rate from fair value on purchase date that participants pay for shares.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=120381028&loc=d3e5070-113901

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- Definition

The estimated dividend rate (a percentage of the share price) to be paid (expected dividends) to holders of the underlying shares over the option's term.

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The estimated measure of the percentage by which a share price is expected to fluctuate during a period. Volatility also may be defined as a probability-weighted measure of the dispersion of returns about the mean. The volatility of a share price is the standard deviation of the continuously compounded rates of return on the share over a specified period. That is the same as the standard deviation of the differences in the natural logarithms of the stock prices plus dividends, if any, over the period.

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The risk-free interest rate assumption that is used in valuing an option on its own shares.

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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- Definition

The weighted average grant-date fair value of options granted during the reporting period as calculated by applying the disclosed option pricing methodology.

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Weighted average per share amount at which grantees can acquire shares of common stock by exercise of options.

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- Definition

Expected term of award under share-based payment arrangement, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days.

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Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
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