The period of time for the trial.

No definition available.

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

- Definition

Amount awarded from other party in judgment or settlement of litigation, that was affirmed by a court of appeals during the period.

+ References

No definition available.

+ Details

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

- Definition

Amount awarded to other party in judgment or settlement of litigation, net of amount awarded from other party.

+ References

No definition available.

+ Details

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

- Definition

Amount awarded to other party in judgment or settlement of litigation, net of amount awarded from other party, affirmed by a court of appeals during the period.

+ References

No definition available.

+ Details

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

- Definition

Number of pending claims remaining after dismissal of the other claims pertaining to a loss contingency.

+ References

No definition available.

+ Details

Name:	ibm_LossContingencyPendingClaimsNumberRemaining
Namespace Prefix:	ibm_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

- Definition

the number of officers or executives of the reporting entity named as defendants.

+ References

No definition available.

+ Details

Name:	ibm_NumberOfOfficerOrExecutivesNamedAsDefendants
Namespace Prefix:	ibm_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount awarded from other party in judgment or settlement of litigation.

+ References

No definition available.

+ Details

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

- Definition

Amount awarded to other party in judgment or settlement of litigation.

+ References

No definition available.

+ Details

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

- Definition

The value (monetary amount) of the award the plaintiff seeks in the legal matter.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 450
-SubTopic 20
-Section 50
-Paragraph 9
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=82911808&loc=d3e14557-108349

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 450
-SubTopic 20
-Section 50
-Paragraph 4
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=82911808&loc=d3e14435-108349

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 450
-SubTopic 20
-Section 50
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=82911808&loc=d3e14326-108349

+ Details

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

- Definition

Number of pending claims pertaining to a loss contingency.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 450
-SubTopic 20
-Section 50
-Paragraph 4
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=82911808&loc=d3e14435-108349

+ Details

Name:	us-gaap_LossContingencyPendingClaimsNumber
Namespace Prefix:	us-gaap_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

- Definition

The number of countries in which the entity operates as of balance sheet date.

+ References

No definition available.

+ Details

Name:	us-gaap_NumberOfCountriesInWhichEntityOperates
Namespace Prefix:	us-gaap_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

- Details

Name:	srt_LitigationCaseAxis=ibm_ScoVsIbmMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_LitigationCaseAxis=ibm_IbmVStateOfIndianaMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_LitigationCaseAxis=ibm_IndividualParticipantsOfDefinedBenefitPlansVsIbmUnitedKingdomMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_LitigationCaseAxis=ibm_LitigationCaseRelatedToViolationsOfEmployeeRetirementIncomeSecurityActInUnitedStatesDistrictCourtRegardingDivestingMicroelectronicsBusinessMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_LossContingenciesByNatureOfContingencyAxis=ibm_BrazilTaxMattersMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_RangeAxis=srt_MinimumMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Contingencies and Commitments - Contingencies (Details) $ in Millions					1 Months Ended	12 Months Ended
	Sep. 28, 2018 USD ($)	Aug. 07, 2017 USD ($)	Feb. 13, 2014 USD ($)	Jul. 18, 2012 USD ($)	May 31, 2015 defendant	Dec. 31, 2018 USD ($) country claim	Oct. 30, 2017 claim
SCO v. IBM
Loss Contingencies
Number of remaining claims \| claim							1
IBM v. State Of Indiana
Loss Contingencies
Duration of trial				42 days
Amount of award to IBM				$ 52
Amount of award to IBM, affirmed by Court of Appeals			$ 50
Amount of award against IBM		$ 128
Net amount awarded against IBM		$ 78
Net amount awarded against IBM, affirmed by Court of Appeals	$ 78
Individual Participants Of Defined Benefit Plans vs. IBM United Kingdom
Loss Contingencies
Claims pending \| claim						290
Litigation Case In United States District Court regarding divesting Microelectronics business, alleging violations of the Employee Retirement Income Security Act
Loss Contingencies
Number of officers or executives named as defendants \| defendant					3
Brazil Tax Matters
Loss Contingencies
Damages sought, value						$ 900
Minimum
Loss Contingencies
Clients' presence in number of countries \| country						175