Taxes (Schedule of Deferred Tax Classification in the Balance Sheet) (Details) - USD ($) $ in Millions	Jan. 31, 2019	Jan. 31, 2018
Liabilities [Abstract]
Net deferred tax liabilities	$ 4,500	$ 1,952
Other assets and deferred charges
Assets
Other assets and deferred charges	1,796	1,879
Deferred income taxes and other
Liabilities [Abstract]
Deferred income taxes and other	$ 6,296	$ 3,831

Amount, after allocation of valuation allowances and deferred tax liability, of deferred tax asset attributable to deductible differences and carryforwards, with jurisdictional netting and classified as noncurrent.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 740
-SubTopic 10
-Section 45
-Paragraph 4
-URI http://asc.fasb.org/extlink&oid=84176650&loc=d3e31917-109318

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 740
-SubTopic 10
-Section 45
-Paragraph 6
-URI http://asc.fasb.org/extlink&oid=84176650&loc=d3e31931-109318

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 740
-SubTopic 10
-Section 50
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=84230637&loc=d3e32537-109319

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant