Accumulated Other Comprehensive Loss (Composition of Accumulated Other Comprehensive Income) (Details) - USD ($) $ in Millions	12 Months Ended
Jan. 31, 2018	Jan. 31, 2017	Jan. 31, 2016
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Balances - beginning of period	$ (14,232)	$ (11,597)	$ (7,168)
Other comprehensive income (loss) before reclassifications	3,960	(2,670)	(4,434)
Amounts reclassified from accumulated other comprehensive income (loss)	91	35	5
Balances - end of period	(10,181)	(14,232)	(11,597)
Currency translation and other
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Balances - beginning of period	(14,507)	(11,690)	(7,011)
Other comprehensive income (loss) before reclassifications	2,345	(2,817)	(4,679)
Amounts reclassified from accumulated other comprehensive income (loss)	26	0	0
Balances - end of period	(12,136)	(14,507)	(11,690)
Net investment hedges
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Balances - beginning of period	1,435	1,022	656
Other comprehensive income (loss) before reclassifications	(405)	413	366
Amounts reclassified from accumulated other comprehensive income (loss)	0	0	0
Balances - end of period	1,030	1,435	1,022
Unrealized gain on available-for-sale securities
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Balances - beginning of period	145	0	0
Other comprehensive income (loss) before reclassifications	1,501	145	0
Amounts reclassified from accumulated other comprehensive income (loss)	0	0	0
Balances - end of period	1,646	145	0
Cash flow hedges
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Balances - beginning of period	(315)	(336)	(134)
Other comprehensive income (loss) before reclassifications	436	(22)	(217)
Amounts reclassified from accumulated other comprehensive income (loss)	1	43	15
Balances - end of period	122	(315)	(336)
Minimum pension liability
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Balances - beginning of period	(990)	(593)	(679)
Other comprehensive income (loss) before reclassifications	83	(389)	96
Amounts reclassified from accumulated other comprehensive income (loss)	64	(8)	(10)
Balances - end of period	$ (843)	$ (990)	$ (593)

A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

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- Definition

Accumulated change in equity from transactions and other events and circumstances from non-owner sources, net of tax effect, at period end. Excludes Net Income (Loss), and accumulated changes in equity from transactions resulting from investments by owners and distributions to owners. Includes foreign currency translation items, certain pension adjustments, unrealized gains and losses on certain investments in debt and equity securities, other than temporary impairment (OTTI) losses related to factors other than credit losses on available-for-sale and held-to-maturity debt securities that an entity does not intend to sell and it is not more likely than not that the entity will be required to sell before recovery of the amortized cost basis, as well as changes in the fair value of derivatives related to the effective portion of a designated cash flow hedge.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 220
-SubTopic 10
-Section 45
-Paragraph 11
-URI http://asc.fasb.org/extlink&oid=84228862&loc=d3e637-108580

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 220
-SubTopic 10
-Section 45
-Paragraph 14
-URI http://asc.fasb.org/extlink&oid=84228862&loc=d3e681-108580

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 220
-SubTopic 10
-Section 45
-Paragraph 14A
-URI http://asc.fasb.org/extlink&oid=84228862&loc=SL7669686-108580

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- Definition

Amount after tax, before reclassification adjustments of other comprehensive income (loss).

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 220
-SubTopic 10
-Section 55
-Paragraph 15
-URI http://asc.fasb.org/extlink&oid=84158357&loc=d3e1436-108581

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 220
-SubTopic 10
-Section 45
-Paragraph 14A
-URI http://asc.fasb.org/extlink&oid=84228862&loc=SL7669686-108580

+ Details

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- Definition

Amount after tax of reclassification adjustments of other comprehensive income (loss).

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 220
-SubTopic 10
-Section 45
-Paragraph 14A
-URI http://asc.fasb.org/extlink&oid=84228862&loc=SL7669686-108580

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 220
-SubTopic 10
-Section 55
-Paragraph 15
-URI http://asc.fasb.org/extlink&oid=84158357&loc=d3e1436-108581

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