Earnings Per Share (Details 1) (USD $)	3 Months Ended		6 Months Ended
	Jul. 31, 2011	Jul. 31, 2010	Jul. 31, 2011	Jul. 31, 2010
Earnings Per Share (Textuals)
Exercise price of warrant sold	$ 74.35	$ 74.35	$ 74.35	$ 74.35
3.625% Puttable Equity-Linked Senior Notes due 2014 [Member]
Debt Instrument [Line Items]
Weighted-average shares issuable upon conversion of the convertible Common Stock Units			13,755,158
3.625% Puttable Equity-Linked Senior Notes due 2011 [Member]
Debt Instrument [Line Items]
Average stock price maximum amount for 2011 Notes to be dilutive	$ 66.39	$ 66.39	$ 66.39	$ 66.39
5.000% Convertible Senior Notes due 2016 [Member]
Debt Instrument [Line Items]
Weighted-average shares issuable upon conversion of the convertible Common Stock Units			5,151,412
4.25% Convertible Senior Notes due 2018 [Member]
Debt Instrument [Line Items]
Weighted-average shares issuable upon conversion of the convertible Common Stock Units			1,159,936
Convertible Preferred Stock [Member]
Debt Instrument [Line Items]
Weighted-average shares issuable upon conversion of the convertible Common Stock Units			14,550,257
Convertible Common Stock [Member]
Debt Instrument [Line Items]
Weighted-average shares issuable upon conversion of the convertible Common Stock Units			3,646,755
Dilutive Options, restricted stock and convertible securities [Member]
Securities Excluded From Computation Of Earnings Per Share [Line Items]
Shares excluded from computation of earnings per shares	39,129,204
Stock Compensation Plan [Member]
Securities Excluded From Computation Of Earnings Per Share [Line Items]
Shares excluded from computation of earnings per shares	3,611,087	5,097,359	3,527,160	4,675,375
Performance Stock [Member]
Securities Excluded From Computation Of Earnings Per Share [Line Items]
Shares excluded from computation of earnings per shares	172,609	172,609	172,609	172,609