Common Share Repurchases and Issuance Activity (Detail) (USD $)	6 Months Ended
	Jul. 31, 2012
Stockholders Equity [Line Items]
Treasury stock held at January 31, 2012, shares	18,166,761
Shares of common stock repurchased under share repurchase program, shares	3,823,217
Shares of treasury stock reissued	(505,686)
Treasury stock held at July 31, 2012, shares	21,484,292
Treasury stock held at January 31, 2012, Weighted-average price per share	$ 40.71
Shares of common stock repurchased under share repurchase program, Weighted-average price per share	$ 49.39
Treasury stock held at July 31, 2012, Weighted-average price per share	$ 42.25