Stock Repurchase Program - Additional Information (Detail) - USD ($)	1 Months Ended	3 Months Ended	8 Months Ended
	Dec. 31, 2014	Jul. 31, 2015	Jul. 31, 2015	Dec. 03, 2013
Equity, Class of Treasury Stock [Line Items]
Stock repurchase program authorized amount		$ 500,000,000	$ 500,000,000	$ 500,000,000
Remaining amount available for further repurchases		200,300,000	200,300,000
Accelerated Share Repurchase Program 2015
Equity, Class of Treasury Stock [Line Items]
Prepayment amount			180,000,000
Prepayment amount, initial share value	$ 144,000,000
Prepayment amount, forward equity contract settled		$ 36,000,000
Shares purchased under agreement			$ 4,000,000
Average purchase price of shares purchased under agreement			$ 45.37
Accelerated Share Repurchase Program 2015 | Common Stock
Equity, Class of Treasury Stock [Line Items]
Stock repurchase program authorized amount	$ 180,000,000