Period up to which the agreement term has been extended.

No definition available.

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

- Definition

The contingent increase above the maximum borrowing capacity under the credit facility, if any one or more of the existing banks or new banks agree to provide such increased commitment amount.

+ References

No definition available.

+ Details

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

- Definition

Period of time between issuance and maturity of debt instrument, in PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ References

No definition available.

+ Details

Name:	us-gaap_DebtInstrumentTerm
Namespace Prefix:	us-gaap_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

The carrying value as of the balance sheet date of the current and noncurrent portions of long-term obligations drawn from a line of credit, which is a bank's commitment to make loans up to a specific amount. Examples of items that might be included in the application of this element may consist of letters of credit, standby letters of credit, and revolving credit arrangements, under which borrowings can be made up to a maximum amount as of any point in time conditional on satisfaction of specified terms before, as of and after the date of drawdowns on the line. Includes short-term obligations that would normally be classified as current liabilities but for which (a) postbalance sheet date issuance of a long term obligation to refinance the short term obligation on a long term basis, or (b) the enterprise has entered into a financing agreement that clearly permits the enterprise to refinance the short-term obligation on a long term basis and the following conditions are met (1) the agreement does not expire within 1 year and is not cancelable by the lender except for violation of an objectively determinable provision, (2) no violation exists at the BS date, and (3) the lender has entered into the financing agreement is expected to be financially capable of honoring the agreement.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02(22))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03(16))
-URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-03(16))
-URI http://asc.fasb.org/extlink&oid=119400593&loc=d3e572229-122910

+ Details

Name:	us-gaap_LineOfCredit
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount of the fee for available but unused credit capacity under the credit facility.

+ References

+ Details

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

- Definition

Date the credit facility terminates, in CCYY-MM-DD format.

+ References

+ Details

Name:	us-gaap_LineOfCreditFacilityExpirationDate1
Namespace Prefix:	us-gaap_
Data Type:	xbrli:dateItemType
Balance Type:	na
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_LineOfCreditFacilityLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Maximum borrowing capacity under the credit facility without consideration of any current restrictions on the amount that could be borrowed or the amounts currently outstanding under the facility.

+ References

+ Details

Name:	us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Details

Name:	us-gaap_CreditFacilityAxis=us-gaap_RevolvingCreditFacilityMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=ibm_FiveYearCreditAgreementMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=ibm_CreditAgreement364Days2018Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=ibm_CreditAgreement364Days2019Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=ibm_CreditAgreement364DaysMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=ibm_ThreeYearCreditAgreementMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=ibm_CreditAgreement364DaysAndThreeYearCreditAgreementMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Borrowings - Lines of Credit (Details) - Credit Facilities - USD ($) $ in Millions		12 Months Ended
	Jul. 18, 2019	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Lines of Credit
Borrowings outstanding		$ 0.0
Five-Year Credit Agreement
Lines of Credit
Amount of credit facility	$ 10,250.0	$ 10,250.0
Credit facility term	5 years	5 years
Extended maturity period	1 year
Credit agreement maturity date	Jul. 20, 2024
Expenses related to the credit facility		$ 7.4	$ 6.7	$ 6.1
Maximum additional amount of commitments under the credit agreement	$ 1,750.0	$ 1,750.0
364-Day Credit Agreement, 2018
Lines of Credit
Amount of credit facility	$ 2,500.0
Credit facility term	364 days
364-Day Credit Agreement, 2019
Lines of Credit
Amount of credit facility	$ 2,500.0
Credit facility term	364 days
364-Day Credit Agreement
Lines of Credit
Credit facility term	364 days	364 days
Three-Year Credit Agreement
Lines of Credit
Amount of credit facility	$ 2,500.0
Credit facility term	3 years	3 years
Extended maturity period	1 year
Credit agreement maturity date	Jul. 20, 2022
364-Day Credit Agreement and Three-Year Credit Agreement
Lines of Credit
Amount of credit facility		$ 5,000.0
Expenses related to the credit facility		$ 2.3	$ 2.1	$ 2.8