Stock Based Compensation (Stock Option Activity) (Details) (USD $) In Millions, except Share data, unless otherwise specified	12 Months Ended
Jan. 31, 2015
Share-based Compensation [Abstract]
Outstanding, beginning of period, shares	23,313,600
Outstanding, beginning of period, weighted average exercise price	$ 32.02
Granted, shares	3,296,000
Granted, weighted average exercise price	$ 58.92
Canceled or forfeited, shares	(468,400)
Canceled or forfeited, weighted average exercise price	$ 41.10
Exercised, shares	(6,462,400)
Exercised, weighted average exercise price	$ 30.98
Outstanding, end of period, shares	19,678,800
Outstanding, end of period, weighted average exercise price	$ 36.65
Exercisable, end of period, shares	11,405,500
Exercisable, end of period, weighted average exercise price	$ 30.06
Exercisable, end of period, weighted average remaining contractual life (years)	4 years
Exercisable, end of period, aggregate intrinsic value	$ 386
Options expected to vest, shares	7,280,500
Options expected to vest, weighted average exercise price	$ 45.73
Options expected to vest, weighted average remaining contractual life (years)	8 years 1 month 6 days
Options expected to vest, aggregate intrinsic value	$ 132

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Amount of difference between fair value of the underlying shares reserved for issuance and exercise price of vested portions of options outstanding and currently exercisable.

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The number of shares into which fully or partially vested stock options outstanding as of the balance sheet date can be currently converted under the option plan.

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The weighted-average price as of the balance sheet date at which grantees can acquire the shares reserved for issuance on vested portions of options outstanding and currently exercisable under the stock option plan.

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Weighted average remaining contractual term for vested portions of options outstanding and currently exercisable or convertible, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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The number of shares under options that were cancelled during the reporting period as a result of occurrence of a terminating event specified in contractual agreements pertaining to the stock option plan.

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Net number of share options (or share units) granted during the period.

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Number of options outstanding, including both vested and non-vested options.

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Weighted average price at which grantees can acquire the shares reserved for issuance under the stock option plan.

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The number of exercisable share options (fully vested and expected to vest) that may be converted as of the balance sheet date.

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Amount by which the current fair value of the underlying stock exceeds the exercise price of fully vested and expected to vest options outstanding.

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As of the balance sheet date, the weighted-average exercise price for outstanding stock options that are fully vested or expected to vest.

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Weighted average remaining contractual term for fully vested and expected to vest options outstanding, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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Weighted average price at which option holders acquired shares when converting their stock options into shares.

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Weighted average price at which grantees could have acquired the underlying shares with respect to stock options that were terminated.

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Weighted average per share amount at which grantees can acquire shares of common stock by exercise of options.

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Number of share options (or share units) exercised during the current period.

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