Fair Value of TSR Performance-Based Awards Valuation Assumption (Detail) - Restricted Stock Units (RSUs) - $ / shares		3 Months Ended		6 Months Ended
		Jan. 31, 2017	Jan. 31, 2016	Jan. 31, 2017	Jan. 31, 2016
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock Price	[1]		$ 81.90	$ 90.23	$ 84.06
Expected volatility	[2]	0.00%	27.60%	27.00%	26.40%
Risk-free interest rate	[3]	0.00%	1.16%	0.85%	1.04%
Expected annual dividend yield	[4]	0.00%	0.00%	0.00%	0.00%
Time Based Restricted Stock Awards
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Weighted average grant date fair value		$ 92.30	$ 81.90	$ 89.48	$ 83.99
Performance Based Restricted Stock Awards
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Weighted average grant date fair value			$ 100.82	$ 87.05	$ 98.81

[1] The stock price is the closing price of our common stock on the date of grant.

[2] The expected volatility for each grant is determined based on the historical volatility for the peer group companies and our common stock over a period equal to the remaining term of the performance period from the date of grant for all awards.

[3] The risk-free interest rate is determined based on the yield of zero-coupon U.S. Treasury securities for a period that is commensurate with the performance period.

[4] Dividends are considered reinvested when calculating TSR. The dividend yield is therefore considered to be 0%.