Shareholders' Equity (Schedule of Fair Value of Restricted Stock) (Details) - USD ($) $ in Millions	12 Months Ended
Jan. 31, 2018	Jan. 31, 2017	Jan. 31, 2016
Restricted stock and performance share units
Additional information related to restricted stock and performance share awards and restricted stock units
Fair value	$ 181	$ 149	$ 142
Unrecognized compensation cost	$ 291	$ 211	$ 133
Weighted average remaining period to expense, years	1 year 2 months	1 year 3 months	1 year 3 months
Restricted stock units
Additional information related to restricted stock and performance share awards and restricted stock units
Fair value	$ 344	$ 261	$ 237
Unrecognized compensation cost	$ 972	$ 986	$ 628
Weighted average remaining period to expense, years	1 year 9 months	1 year 11 months	1 year 8 months

Unrecognized cost of unvested share-based awards, other than options, awarded to employees as compensation.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (i)
-URI http://asc.fasb.org/extlink&oid=96867065&loc=d3e5070-113901

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- Definition

Weighted average remaining contractual term for equity-based awards excluding options, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (e)(1)
-URI http://asc.fasb.org/extlink&oid=96867065&loc=d3e5070-113901

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- Definition

Fair value of share-based awards for which the grantee gained the right by satisfying service and performance requirements, to receive or retain shares or units, other instruments, or cash.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (d)(2)
-URI http://asc.fasb.org/extlink&oid=96867065&loc=d3e5070-113901

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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.

+ References

No definition available.

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