Stockholders' equity (deficit) (Details) (USD $)	9 Months Ended		1 Months Ended						1 Months Ended			3 Months Ended	9 Months Ended
	Jul. 31, 2012	Jul. 31, 2011	Sep. 30, 2011 Maximum [Member]	Nov. 30, 2011 Accelerated Share Repurchases Program [Member]	Oct. 31, 2011 Accelerated Share Repurchases Program [Member]	Oct. 31, 2011 October 2011 [Member]	Oct. 31, 2011 October 2011 [Member] Accelerated Share Repurchases Program [Member]	Oct. 31, 2011 November 2011 [Member]	Nov. 30, 2011 November 2011 [Member] Accelerated Share Repurchases Program [Member]	Jan. 31, 2012 Open Market Share Repurchase Program [Member]	Oct. 31, 2011 Open Market Share Repurchase Program [Member]	Jul. 31, 2012 Open Market Share Repurchase Program [Member]	Jul. 31, 2012 Open Market Share Repurchase Program [Member] Repurchase of Equity [Member]
Class of Stock [Line Items]
Exercise Price Stockholder Rights Plan	$ 140.00
Redeemable amount per right under Shareholder Rights Plan	0
Ownership Percentage Stockholder Rights Plan	15.00%
Stock Repurchase Program, Authorized Amount			175,000,000		100,000,000
Payments for Repurchase of Common Stock	75,000,000	11,000,000			100,000,000
Treasury Stock, Shares, Acquired				2,542,609			2,380,952			1,905,600
Accelerated Share Repurchases, Settlement Payment or Receipt						80,000,000		20,000,000
Accelerated Share Repurchases, Initial Price Paid Per Share						$ 33.60
Stock Repurchase Program, Remaining Authorized Repurchase Amount					$ 20,000,000						$ 75,000,000	$ 70,000,000	$ 5,000,000
Treasury Stock, Additional Shares Acquired									161,657