Stock-based Compensation Expense Stock-Based Compensation Expense - Additional Information (Details) (USD $) In Millions, except Share data, unless otherwise specified	3 Months Ended		6 Months Ended
	Jul. 31, 2012 StockPlans	Jul. 31, 2011	Jul. 31, 2012 StockPlans		Jul. 31, 2011
Compensation Related Costs Share Based Payments Disclosure [Line Items]
Share based compensation arragements by share based payment awards, number of active plans (presented as an integer)	2		2
Share based compensation arrangement by share based payment award expired or terminated plans (presented as an integer)	8		8
Share-Based Compensation Shares Granted to Share Issued			$ 2.11
Employee Service Share-based Compensation, Nonvested Awards, Total Compensation Cost Not yet Recognized (in usd)	$ 54.9		$ 54.9
Share Based Compensation Non Vested Options Outstanding Weighted Average Remaining Contractual Term (in years)	1 year 6 months		1 year 6 months
Sale of Stock, Price Per Share (in usd per share)	$ 33.92		$ 33.92
Employee Service Share Based Compensation Unrecognized Compensation Costs On Nonvested Restricted Shares (in usd)	54.9		54.9
Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Weighted Average Grant Date Fair Value (in usd per share)	$ 10.86	$ 11.95	$ 13.40	[1]	$ 14.26
Employee Stock Plan 2012 [Member]
Compensation Related Costs Share Based Payments Disclosure [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Authorized	21,200,000		21,200,000
Stock Issued During Period, Shares, Restricted Stock Award, Net of Forfeitures			15,200,000
Stock Issued During Period, Shares, Share-based Compensation, Forfeited			6,000,000
Share-Based Compensation Shares Granted to Share Issued			$ 1.79
Number of options or stock units granted in a plan to-date	5,700,000		5,700,000
Share Based Compensation Arrangement By Share Based Payment Award Maximum Vesting Period For Stock Options (in years)	3 years		3 years
Employee Stock Plan Shares Remaining Available For Issuance	11,400,000		11,400,000
Employee Stock Plan 2012 [Member] | Maximum [Member]
Compensation Related Costs Share Based Payments Disclosure [Line Items]
Share based compensation arrangement by share based payment award options expiration term (in years)			10 years
Directors stock plan 2012 [Member]
Compensation Related Costs Share Based Payments Disclosure [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Authorized	2,600,000		2,600,000
Number of options or stock units granted in a plan to-date	200,000		200,000
Share Based Compensation Arrangement By Share Based Payment Award Maximum Vesting Period For Stock Options (in years)	1 year		1 year
Employee Stock Plan Shares Remaining Available For Issuance	2,400,000		2,400,000
Employee Qualified Stock Purchase Plan 1998 ESP Plan [Member]
Compensation Related Costs Share Based Payments Disclosure [Line Items]
Employee Stock Plan Shares Remaining Available For Issuance	32,900,000		32,900,000
Employee Stock Purchase Plan Maximum Percentage Of Compensation To Purchase Shares By Eligible Participants (presented as a percent)			15.00%
Employee Stock Purchase Plan Minimum Percentage Of Common Stock Fair Value Defined To Purchase Shares By Eligible Participants (presented as a percent)			85.00%
Share-based Compensation Arrangement by Share-based Payment Award, Options, Other Increases (Decreases) in Period			10,000,000
Share Based Compensation Arrangement By Share Based Payment Award Options Other Increases Decreases In Period Percentage Calculation (presented as a percent)			2.00%
Stock Issued During Period, Shares, Employee Stock Purchase Plans			1,600,000		1,800,000
Share Based Compensation Arrangement By Share Based Payment Award Shares Issued Average Price (in usd per share)			$ 21.63		$ 15.28
Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Weighted Average Grant Date Fair Value (in usd per share)			$ 14.00		$ 13.46
Restricted Stock Units (RSUs) [Member]
Compensation Related Costs Share Based Payments Disclosure [Line Items]
Period for Recognition, Employee Service Share-Based Compensation, Nonvested Awards, Total Compensation Cost Not Yet Recognized			2 years
Employee Service Share-based Compensation, Nonvested Awards, Total Compensation Cost Not yet Recognized (in usd)	100.7		100.7
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period			2,600,000
Allocated Share-based Compensation Expense (in usd)	12.5	8.3	23.3		13.6
Employee Service Share Based Compensation Unrecognized Compensation Costs On Nonvested Restricted Shares (in usd)	100.7		100.7
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number	4,500,000		4,500,000
Performance Shares [Member]
Compensation Related Costs Share Based Payments Disclosure [Line Items]
Period for Recognition, Employee Service Share-Based Compensation, Nonvested Awards, Total Compensation Cost Not Yet Recognized			1 year 7 months 6 days
Employee Service Share-based Compensation, Nonvested Awards, Total Compensation Cost Not yet Recognized (in usd)	10.3		10.3
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period			500,000
Allocated Share-based Compensation Expense (in usd)	2.1		3.3		0
Employee Service Share Based Compensation Unrecognized Compensation Costs On Nonvested Restricted Shares (in usd)	$ 10.3		$ 10.3
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number	500,000		500,000

[1] The weighted average grant date fair value of stock options granted is calculated, as of the stock option grant date, using the Black-Scholes-Merton option pricing model.