Earnings per Share (Details) (USD $)	1 Months Ended	2 Months Ended	3 Months Ended		6 Months Ended		10 Months Ended
	Oct. 31, 2010	Jul. 31, 2011	Nov. 30, 2011	Nov. 30, 2010	Nov. 30, 2011	Nov. 30, 2010	Jul. 29, 2011	Oct. 18, 2011
Basic Earnings per Share
Net income			$ 74,350,000	$ 55,866,000	$ 142,988,000	$ 117,143,000
Less dividends to:
Total dividends			70,820,000	71,880,000	70,820,000	71,880,000
Undistributed net income (loss)			3,530,000	(16,014,000)	72,168,000	45,263,000
Less: net income (loss) allocated to participating unvested securities			21,000	(74,000)	448,000	204,000
Net income (loss) available to common shareholders			3,509,000	(15,940,000)	71,720,000	45,059,000
Basic weighted average common shares outstanding (in shares)			129,727,000	145,511,000	130,522,000	148,856,000
Basic earnings per share:
Total shares (in dollars per share)			$ 0.57	$ 0.38	$ 1.09	$ 0.78
Diluted Earnings per Share
Net income			74,350,000	55,866,000	142,988,000	117,143,000
Less dividends to:
Total dividends			70,820,000	71,880,000	70,820,000	71,880,000
Undistributed net income (loss)			3,530,000	(16,014,000)	72,168,000	45,263,000
Less: net income (loss) allocated to participating unvested securities			21,000	(74,000)	448,000	204,000
Net income (loss) available to common shareholders			3,509,000	(15,940,000)	71,720,000	45,059,000
Basic weighted average common shares outstanding (in shares)			129,727,000	145,511,000	130,522,000	148,856,000
Effect of dilutive securities - employee stock options (in shares)			13,000		21,000
Diluted weighted average common shares outstanding (in shares)			129,740,000	145,511,000	130,543,000	148,856,000
Diluted earnings per share:
Total shares (in dollars per share)			$ 0.57	$ 0.38	$ 1.09	$ 0.78
Options granted excluded from the computation of diluted earnings per share (in shares)			3,300,000	3,500,000	2,600,000	3,900,000
Additional amount authorized under share buyback program	500,000,000
Common stock purchased under a share buyback program (in shares)		8,100,000					15,800,000
Aggregate purchase price of common stock under a share buyback program		259,500,000
Average price of common stock purchased under a share buyback program (in dollars per share)							$ 31.70
New amount authorized under share buyback program								500,000,000
Common shares
Less dividends to:
Total dividends			70,055,000	71,197,000	70,055,000	71,197,000
Basic earnings per share:
Distributed earnings (in dollars per share)			$ 0.54	$ 0.49	$ 0.54	$ 0.49
Undistributed earnings (in dollars per share)			$ 0.03	$ (0.11)	$ 0.55	$ 0.29
Total shares (in dollars per share)			$ 0.57	$ 0.38	$ 1.09	$ 0.78
Less dividends to:
Total dividends			70,055,000	71,197,000	70,055,000	71,197,000
Diluted earnings per share:
Distributed earnings (in dollars per share)			$ 0.54	$ 0.49	$ 0.54	$ 0.49
Undistributed earnings (in dollars per share)			$ 0.03	$ (0.11)	$ 0.55	$ 0.29
Total shares (in dollars per share)			$ 0.57	$ 0.38	$ 1.09	$ 0.78
Unvested shares
Less dividends to:
Total dividends			765,000	683,000	765,000	683,000
Basic earnings per share:
Distributed earnings (in dollars per share)			$ 0.54	$ 0.49	$ 0.54	$ 0.49
Undistributed earnings (in dollars per share)			$ 0.03	$ (0.11)	$ 0.55	$ 0.29
Total shares (in dollars per share)			$ 0.57	$ 0.38	$ 1.09	$ 0.78
Less dividends to:
Total dividends			$ 765,000	$ 683,000	$ 765,000	$ 683,000
Diluted earnings per share:
Distributed earnings (in dollars per share)			$ 0.54	$ 0.49	$ 0.54	$ 0.49
Undistributed earnings (in dollars per share)			$ 0.03	$ (0.11)	$ 0.55	$ 0.29
Total shares (in dollars per share)			$ 0.57	$ 0.38	$ 1.09	$ 0.78