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Share-Based Payments (Details) - USD ($)	12 Months Ended
	Aug. 31, 2019	Aug. 31, 2018	Aug. 31, 2017	Jan. 31, 2018	Aug. 31, 2016
Share-based Compensation Arrangement, Restricted Stock Awards [Abstract]
Share-based expense	$ 29,200,000	$ 32,300,000	$ 32,000,000.0
Stock Options | $40.01 - $100.00 (average life - 3.1 years)
Share-based Payment Arrangement, Option, Exercise Price Range, End of Period [Abstract]
Range of option exercise prices: lower range limit (in dollars per share)	$ 40.01
Range of option exercise prices: upper range limit (in dollars per share)	$ 100
Range of option exercise prices: average life	3 years 1 month
Stock Options | $100.01 - $160.00 (average life - 6.9 years)
Share-based Payment Arrangement, Option, Exercise Price Range, End of Period [Abstract]
Range of option exercise prices: lower range limit (in dollars per share)	$ 100.01
Range of option exercise prices: upper range limit (in dollars per share)	$ 160
Range of option exercise prices: average life	6 years 10 months 24 days
Stock Options | $160.01 - $210.00 (average life - 6.2 years)
Share-based Payment Arrangement, Option, Exercise Price Range, End of Period [Abstract]
Range of option exercise prices: lower range limit (in dollars per share)	$ 160.01
Range of option exercise prices: upper range limit (in dollars per share)	$ 210
Range of option exercise prices: average life	6 years 2 months 12 days
Stock Options | $210.01 - $239.76 (average life - 7.1 years)
Share-based Payment Arrangement, Option, Exercise Price Range, End of Period [Abstract]
Range of option exercise prices: lower range limit (in dollars per share)	$ 210.01
Range of option exercise prices: upper range limit (in dollars per share)	$ 239.76
Range of option exercise prices: average life	7 years 1 month
Restricted Stock
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward]
Forfeited (in shares)	0
Weighted Average Grant Date Fair Value Per Share [Roll Forward]
Forfeited, Weighted Average Grant Date Fair Value Per Share (in dollars per share)	$ 159.88
Stock Incentive Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares authorized for issuance (in shares)				2,700,000
Number of shares available for grant (in shares)	1,400,000	1,600,000	1,400,000
Stock Incentive Plan | $40.01 - $100.00 (average life - 3.1 years)
Share-based Payment Arrangement, Option, Exercise Price Range, End of Period [Abstract]
Range of option exercise prices: Number of Shares, Outstanding	100,000
Range of option exercise prices: Weighted Average Exercise Price, Outstanding (in dollars per share)	$ 62.25
Range of option exercise prices: Number of Shares, Exercisable	100,000
Range of option exercise prices: Weighted Average Exercise Price, Exercisable (in dollars per share)	$ 62.25
Stock Incentive Plan | $100.01 - $160.00 (average life - 6.9 years)
Share-based Payment Arrangement, Option, Exercise Price Range, End of Period [Abstract]
Range of option exercise prices: Number of Shares, Outstanding	200,000
Range of option exercise prices: Weighted Average Exercise Price, Outstanding (in dollars per share)	$ 125.66
Range of option exercise prices: Number of Shares, Exercisable	100,000
Range of option exercise prices: Weighted Average Exercise Price, Exercisable (in dollars per share)	$ 125.09
Stock Incentive Plan | $160.01 - $210.00 (average life - 6.2 years)
Share-based Payment Arrangement, Option, Exercise Price Range, End of Period [Abstract]
Range of option exercise prices: Number of Shares, Outstanding	100,000
Range of option exercise prices: Weighted Average Exercise Price, Outstanding (in dollars per share)	$ 207.80
Range of option exercise prices: Number of Shares, Exercisable	100,000
Range of option exercise prices: Weighted Average Exercise Price, Exercisable (in dollars per share)	$ 207.80
Stock Incentive Plan | $210.01 - $239.76 (average life - 7.1 years)
Share-based Payment Arrangement, Option, Exercise Price Range, End of Period [Abstract]
Range of option exercise prices: Number of Shares, Outstanding	100,000
Range of option exercise prices: Weighted Average Exercise Price, Outstanding (in dollars per share)	$ 239.76
Range of option exercise prices: Number of Shares, Exercisable	0
Range of option exercise prices: Weighted Average Exercise Price, Exercisable (in dollars per share)	$ 239.76
Stock Incentive Plan | Stock Options
Share-based Compensation Arrangement, Restricted Stock Awards [Abstract]
Share-based compensation vesting period (years)	3 years
Share-based expense	$ 2,700,000	$ 3,100,000	$ 3,600,000
Weighted Average Grant Date Fair Value Per Share [Roll Forward]
Unrecognized compensation cost	$ 2,800,000
Unrecognized compensation cost period of recognition (years)	1 year 3 months 18 days
Share-based Compensation Arrangement, Stock Options [Abstract]
Share-based compensation, expiration period	10 years
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions and Methodology [Abstract]
Dividend yield	0.40%	0.30%	0.20%
Expected volatility	32.80%	30.90%	28.50%
Risk-free interest rate	3.00%	2.00%	1.30%
Expected life of options	4 years	4 years	4 years
Weighted-average fair value of options (in dollars per share)	$ 34.06	$ 41.87	$ 57.40
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward]
Beginning of period, Outstanding, Number of Shares	300,000	300,000	300,000
Granted, Number of Shares	100,000	0	0
Stock options exercised (in shares)	0	0	0
End of period, Outstanding, Number of Shares	420,000	300,000	300,000
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price [Roll Forward]
Beginning of period, Outstanding, Weighted average exercise price (in dollars per share)	$ 154.69	$ 156.43	$ 129.85
Granted, Weighted average exercise price (in dollars per share)	116.40	156.39	239.76
Exercised, Weighted average exercise price (in dollars per share)		115.27	139.69
End of period, Outstanding, Weighted average exercise price (in dollars per share)	$ 146.70	$ 154.69	$ 156.43
Exercisable, Number of shares outstanding (in shares)	300,000	200,000	200,000		100,000
Exercisable, Weighted average exercise price (in dollars per share)	$ 147.51	$ 134.13	$ 106.54		$ 83.89
Share-based Payment Arrangement, Option, Exercise Price Range, End of Period [Abstract]
Total intrinsic value of stock options expected to vest		$ 500,000	$ 1,300,000
Stock options exercised (in shares)	0	0	0
Total intrinsic value of stock options outstanding	$ 5,800,000
Total intrinsic value of stock options expected to vest	700,000
Total intrinsic value of stock options exercisable	$ 5,100,000
Stock Incentive Plan | Restricted Stock
Share-based Compensation Arrangement, Restricted Stock Awards [Abstract]
Share-based compensation vesting period (years)	4 years
Share-based expense	$ 25,100,000	$ 27,900,000	$ 27,200,000
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward]
Beginning of period, Outstanding (in shares)	400,000
Granted (in shares)	200,000
Vested (in shares)	(200,000)
End of period, Outstanding (in shares)	350,000	400,000
Weighted Average Grant Date Fair Value Per Share [Roll Forward]
Beginning of period, Outstanding, Weighted Average Grant date Fair Value Per Share (in dollars per share)	$ 186.63
Granted, Weighted Average Grant Date Fair Value Per Share (in dollars per share)	120.73
Vested, Weighted Average Grant Date Fair Value Per Share (in dollars per share)	184.60
End of period, Outstanding, Weighted Average Grant Date Fair Value Per Share (in dollars per share)	$ 156.32	$ 186.63
Unrecognized compensation cost	$ 34,600,000
Unrecognized compensation cost period of recognition (years)	1 year 7 months 6 days
Total fair value of shares vested	$ 26,900,000	$ 26,600,000	24,800,000
Supplemental Deferred Savings Plan | Restricted Stock Units (RSUs)
Share-based Compensation Arrangement, Restricted Stock Awards [Abstract]
Share-based expense	$ 0	$ 0	$ 0
Share-based Payment Arrangement, Option, Exercise Price Range, End of Period [Abstract]
Deferred compensation, number of share units outstanding	9,000
Directors' Deferred Compensation Plan | Restricted Stock Units (RSUs)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares available for grant (in shares)	360,000	370,000	390,000
Share-based Compensation Arrangement, Restricted Stock Awards [Abstract]
Share-based expense	$ 1,400,000	$ 1,300,000	$ 1,200,000
Share-based Payment Arrangement, Option, Exercise Price Range, End of Period [Abstract]
Deferred compensation, number of share units outstanding	119,000
Employee Stock Purchase Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares authorized for issuance (in shares)	1,500,000
Number of shares available for grant (in shares)	1,000,000.0
Share-based Payment Arrangement, Option, Exercise Price Range, End of Period [Abstract]
Employee discount on purchases of common stock	5.00%

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Amount of expense for award under share-based payment arrangement. Excludes amount capitalized.

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Period over which grantee's right to exercise award under share-based payment arrangement is no longer contingent on satisfaction of service or performance condition, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days. Includes, but is not limited to, combination of market, performance or service condition.

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

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Weighted average fair value as of the grant date of equity-based award plans other than stock (unit) option plans that were not exercised or put into effect as a result of the occurrence of a terminating event.

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Per share or unit weighted-average fair value of nonvested award under share-based payment arrangement. Excludes share and unit options.

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Fair value of share-based awards for which the grantee gained the right by satisfying service and performance requirements, to receive or retain shares or units, other instruments, or cash.

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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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