Plan Assets Held in Trust (Detail)	12 Months Ended
	Jul. 31, 2012	Jul. 31, 2011
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Target allocation percentage	100.00%
Actual allocation percentage	100.00%	100.00%
Equity securities
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Target allocation percentage	65.00%
Actual allocation percentage	65.60%	63.00%
Debt securities
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Target allocation percentage	35.00%
Actual allocation percentage	34.40%	37.00%