Shareholders' Equity (Schedule of Share Repurchases) (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	12 Months Ended
Jan. 31, 2018	Jan. 31, 2017	Jan. 31, 2016
Share Repurchases [Abstract]
Total number of shares repurchased	104.9	119.9	62.4
Average price paid per share	$ 79.11	$ 69.18	$ 65.90
Total amount paid for share repurchases	$ 8,296	$ 8,298	$ 4,112

Equity impact of the cost of common and preferred stock that were repurchased during the period. Recorded using the cost method.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section 50
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=84159872&loc=d3e21463-112644

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 30
-Section 45
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=6405813&loc=d3e23239-112655

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.3-04)
-URI http://asc.fasb.org/extlink&oid=27012166&loc=d3e187085-122770

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