Amount of cash which is expected to be remitted in the future period.

No definition available.

Name:	ibm_DisposalGroupIncludingDiscontinuedOperationAmountExpectedToPay
Namespace Prefix:	ibm_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount of consideration expected to receive relating to the disposal of assets and liabilities, including discontinued operation.

+ References

No definition available.

+ Details

Name:	ibm_DisposalGroupIncludingDiscontinuedOperationConsiderationExpectedToReceive
Namespace Prefix:	ibm_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

The cash inflow associated with the amount received from contingent consideration during the period.

+ References

No definition available.

+ Details

Name:	ibm_DisposalGroupIncludingDiscontinuedOperationConsiderationReceived
Namespace Prefix:	ibm_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Amount of contingent consideration included in the total relating to the disposal of assets and liabilities.

+ References

No definition available.

+ Details

Name:	ibm_DisposalGroupIncludingDiscontinuedOperationContingentConsiderationIncludedInTotal
Namespace Prefix:	ibm_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Period of time in which the company expects to receive outstanding contingent consideration.

+ References

No definition available.

+ Details

Name:	ibm_DisposalGroupIncludingDiscontinuedOperationExpectedDurationToReceiveOutstandingContingentConsideration
Namespace Prefix:	ibm_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount which is remitted for servicing customer contracts.

+ References

No definition available.

+ Details

Name:	ibm_DisposalGroupIncludingDiscontinuedOperationPaymentsForServicingCustomerContracts
Namespace Prefix:	ibm_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Period after closing for receipt of the remaining cash consideration from the sale of a portion of the company's business.

+ References

No definition available.

+ Details

Name:	ibm_DisposalGroupIncludingDiscontinuedOperationPeriodForReceiptOfRemainingConsideration
Namespace Prefix:	ibm_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount of consideration received or receivable for the disposal of assets and liabilities, including discontinued operation.

+ References

No definition available.

+ Details

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

- Definition

Amount before tax of gain (loss) recognized on the sale or disposal of a disposal group. Excludes discontinued operations.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 360
-SubTopic 10
-Section 45
-Paragraph 5
-URI http://asc.fasb.org/extlink&oid=109226348&loc=d3e2443-110228

Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 28
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=118932676&loc=d3e3602-108585

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 360
-SubTopic 10
-Section 50
-Paragraph 3
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=109226691&loc=d3e2941-110230

+ Details

Name:	us-gaap_DisposalGroupNotDiscontinuedOperationGainLossOnDisposal
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- 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.

+ Details

Name:	us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

The cash inflow associated with the amount received from the sale of a portion of the company's business, for example a segment, division, branch or other business, during the period.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 12
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=118932676&loc=d3e3179-108585

+ Details

Name:	us-gaap_ProceedsFromDivestitureOfBusinesses
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Details

Name:	us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis=ibm_SelectStandaloneCloudAndCognitiveSoftwareProductsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis=ibm_SelectMarketingPlatformAndCommerceOfferingsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_StatementGeographicalAxis=country_US
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis=ibm_SalesPerformanceManagementOfferingsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Acquisitions/Divestitures - Divestitures (Details) - USD ($) $ in Millions		3 Months Ended		6 Months Ended	12 Months Ended
	Jun. 30, 2019	Mar. 31, 2020	Sep. 30, 2019	Jun. 30, 2019	Dec. 31, 2019
Select Standalone Cloud and Cognitive Software Products
Divestitures
Consideration	$ 1,775			$ 1,775
Contingent consideration included in total	$ 150			150
Cash consideration received		$ 164		812
Contingent consideration received			$ 40
Remaining consideration to be received		648
Pre-tax gain on sale of business		625
Cash remitted		(139)
Cash expected to be remitted in 2021		$ (185)
Period after closing to receive outstanding contingent consideration	24 months
Select Marketing Platform and Commerce Offerings \| U.S.
Divestitures
Cash consideration received	$ 240
Remaining consideration to be received	$ 150			$ 150
Period after closing for receipt of remaining consideration	36 months
Sales Performance Management Offerings
Divestitures
Cash consideration received					$ 230
Pre-tax gain on sale of business					$ 136