Represents the expense recognized during the period arising from equity-based compensation arrangements (for example, shares of stock, unit, stock options or other equity instruments) with employees, directors and certain consultants qualifying for treatment as employees.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
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- Definition

The total recognized tax benefit related to compensation cost for equity-based payment arrangements recognized in income during the period.

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Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
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- Definition

Period which an employee's right to exercise an award is no longer contingent on satisfaction of either a service condition, market condition or a performance condition, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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Reference 1: http://www.xbrl.org/2003/role/presentationRef
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- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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No definition available.

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- Definition

The maximum number of shares (or other type of equity) originally approved (usually by shareholders and board of directors), net of any subsequent amendments and adjustments, for awards under the equity-based compensation plan. As stock or unit options and equity instruments other than options are awarded to participants, the shares or units remain authorized and become reserved for issuance under outstanding awards (not necessarily vested).

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
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- Definition

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

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- Definition

Amount of stock repurchase plan authorized.

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Amount remaining of a stock repurchase plan authorized.

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- Definition

Share-based Compensation Arrangement by Share-based Payment Award, Vesting Percentage

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ShareBasedCompensationArrangementByShareBasedPaymentAwardVestingPercentageYear3 - Percentage of grant that vest in the 3rd year.

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Sharebasedcompensationarrangementbysharebasedpaymentawardvestingpercentageyear5 - percentage of grant that vest in year 5.

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- Definition

Weighted Average Discount For Dividend Yield

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Shareholders' Equity (Details) - USD ($) shares in Thousands, $ in Millions	12 Months Ended
	Jan. 31, 2018	Jan. 31, 2017	Jan. 31, 2016	Oct. 09, 2017	Jun. 05, 2015
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation expense	$ 626	$ 596	$ 448
Income tax benefit recognized for share-based compensation	150	212	151
Number of shares registered under the Securities Act of 1933					210,000
Restricted stock and performance share units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation expense	$ 234	$ 237	$ 134
Shares, granted	3,598
Restricted stock and performance share units \| Minimum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Restricted stock and performance share awards vesting percentages	0.00%
Restricted stock, performance share awards and stock option plans vesting periods, in years	1 year
Restricted stock and performance share units \| Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Restricted stock and performance share awards vesting percentages	150.00%
Restricted stock, performance share awards and stock option plans vesting periods, in years	3 years
Performance Shares [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Weighted average discount for dividend yield	7.20%	8.30%	7.40%
Restricted stock units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation expense	$ 368	$ 332	$ 292
Weighted average discount for dividend yield	9.00%	9.00%	8.70%
Restricted stock units vesting percentage, 3 years	50.00%
Restricted stock units vesting percentage, 5 years	50.00%
Shares, granted	8,570
Restricted stock units \| Minimum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Restricted stock, performance share awards and stock option plans vesting periods, in years	3 years
Restricted stock units \| Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Restricted stock, performance share awards and stock option plans vesting periods, in years	5 years
Employee Stock Option [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Restricted stock, performance share awards and stock option plans vesting periods, in years	3 years
Two Thousand And Seventeen Share Repurchase Program [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share repurchase program, authorized amount				$ 20,000
Stock repurchase program, remaining authorized repurchase amount	$ 18,800