Earnings per Share (Details) (USD $)	1 Months Ended	2 Months Ended	3 Months Ended		9 Months Ended		10 Months Ended
	Oct. 31, 2010	Jul. 31, 2011	Feb. 29, 2012	Feb. 28, 2011	Feb. 29, 2012	Feb. 28, 2011	Jul. 29, 2011	Oct. 18, 2011
Basic Earnings per Share
Net income			$ 76,035,000	$ 59,070,000	$ 219,023,000	$ 176,213,000
Less dividends to:
Total dividends					70,820,000	71,812,000
Undistributed net income			76,035,000	59,070,000	148,203,000	104,401,000
Less: net income allocated to participating unvested securities			556,000	316,000	1,096,000	564,000
Net income available to common shareholders			75,479,000	58,754,000	147,107,000	103,837,000
Basic weighted average common shares outstanding			129,735,000	145,303,000	130,261,000	147,686,000
Basic earnings per share:
Total shares (in dollars per share)			$ 0.58	$ 0.41	$ 1.67	$ 1.19
Diluted Earnings per Share
Net income			76,035,000	59,070,000	219,023,000	176,213,000
Less dividends to:
Total dividends					70,820,000	71,812,000
Undistributed net income			76,035,000	59,070,000	148,203,000	104,401,000
Less: net income allocated to participating unvested securities			556,000	316,000	1,096,000	564,000
Net income available to common shareholders			75,479,000	58,754,000	147,107,000	103,837,000
Basic weighted average common shares outstanding			129,735,000	145,303,000	130,261,000	147,686,000
Effect of dilutive securities - employee stock options (in shares)			210,000		60,000
Diluted weighted average common shares outstanding			129,945,000	145,303,000	130,321,000	147,686,000
Diluted earnings per share:
Total shares (in dollars per share)			$ 0.58	$ 0.41	$ 1.67	$ 1.19
Options granted excluded from the computation of diluted earnings per share (in shares)			1,100,000	3,500,000	2,100,000	3,600,000
Additional amount authorized under share buyback program	500,000,000
Common stock purchased under a share buyback program		8,100,000					15,800,000
Aggregate purchase price of common stock under a share buyback program		259,500,000					500,000,000
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
Basic earnings per share:
Distributed earnings (in dollars per share)			$ 0.00	$ 0.00	$ 0.54	$ 0.49
Undistributed earnings (in dollars per share)			$ 0.58	$ 0.41	$ 1.13	$ 0.70
Total shares (in dollars per share)			$ 0.58	$ 0.41	$ 1.67	$ 1.19
Less dividends to:
Total dividends					70,055,000	71,197,000
Diluted earnings per share:
Distributed earnings (in dollars per share)			$ 0.00	$ 0.00	$ 0.54	$ 0.49
Undistributed earnings (in dollars per share)			$ 0.58	$ 0.41	$ 1.13	$ 0.70
Total shares (in dollars per share)			$ 0.58	$ 0.41	$ 1.67	$ 1.19
Unvested shares
Less dividends to:
Total dividends					765,000	615,000
Basic earnings per share:
Distributed earnings (in dollars per share)			$ 0.00	$ 0.00	$ 0.54	$ 0.49
Undistributed earnings (in dollars per share)			$ 0.58	$ 0.41	$ 1.13	$ 0.70
Total shares (in dollars per share)			$ 0.58	$ 0.41	$ 1.67	$ 1.19
Less dividends to:
Total dividends					$ 765,000	$ 615,000
Diluted earnings per share:
Distributed earnings (in dollars per share)			$ 0.00	$ 0.00	$ 0.54	$ 0.49
Undistributed earnings (in dollars per share)			$ 0.58	$ 0.41	$ 1.13	$ 0.70
Total shares (in dollars per share)			$ 0.58	$ 0.41	$ 1.67	$ 1.19