Financial Instruments: (Details 3) (USD $) In Millions, unless otherwise specified	3 Months Ended
Mar. 31, 2013 basispoint	Dec. 31, 2012
Financial Instruments:
Derivative instruments with credit-risk related contingent features	$ 16	$ 94
Collateral posted on derivative instruments	0	0
Fair Values of Derivative Instruments
Fair value of total derivative instruments, Assets	1,061	918
Fair value of total derivative instruments, Liabilities	3,767	4,116
Maximum spread on credit default swap agreements before full overnight collateralization is required (in basis points)	250
Liabilities included in master netting arrangements	220	262
Cash collateral received, derivatives	151	69
Net exposure related to derivative assets recorded in the Statement of Financial Position	690	587
Net amount related to derivative liabilities recorded in the Statement of Financial Position	76	242
Non-cash collateral received and not recorded on the Statement of Financial Position	21	31
Cash collateral rehypothecated	0	0
Derivative instruments designated as hedging instruments
Fair Values of Derivative Instruments
Fair value of total derivative instruments, Assets	908	744
Fair value of total derivative instruments, Liabilities	190	345
Derivative instruments not designated as hedging instruments
Fair Values of Derivative Instruments
Fair value of total derivative instruments, Assets	153	174
Fair value of total derivative instruments, Liabilities	106	159
Other receivables
Fair Values of Derivative Instruments
Cash collateral issued, derivatives	0	0
Accounts payable
Fair Values of Derivative Instruments
Cash collateral received, derivatives	151	69
Prepaid expenses and other current assets \| Interest rate contracts \| Derivative instruments designated as hedging instruments
Fair Values of Derivative Instruments
Fair value of total derivative instruments, Assets	66	47
Prepaid expenses and other current assets \| Foreign exchange contracts \| Derivative instruments designated as hedging instruments
Fair Values of Derivative Instruments
Fair value of total derivative instruments, Assets	317	135
Prepaid expenses and other current assets \| Foreign exchange contracts \| Derivative instruments not designated as hedging instruments
Fair Values of Derivative Instruments
Fair value of total derivative instruments, Assets	110	142
Prepaid expenses and other current assets \| Equity contracts \| Derivative instruments not designated as hedging instruments
Fair Values of Derivative Instruments
Fair value of total derivative instruments, Assets	26	9
Investments and sundry assets \| Interest rate contracts \| Derivative instruments designated as hedging instruments
Fair Values of Derivative Instruments
Fair value of total derivative instruments, Assets	518	557
Investments and sundry assets \| Foreign exchange contracts \| Derivative instruments designated as hedging instruments
Fair Values of Derivative Instruments
Fair value of total derivative instruments, Assets	7	5
Investments and sundry assets \| Foreign exchange contracts \| Derivative instruments not designated as hedging instruments
Fair Values of Derivative Instruments
Fair value of total derivative instruments, Assets	17	23
Other accrued expenses and liabilities \| Foreign exchange contracts \| Derivative instruments designated as hedging instruments
Fair Values of Derivative Instruments
Fair value of total derivative instruments, Liabilities	132	267
Other accrued expenses and liabilities \| Foreign exchange contracts \| Derivative instruments not designated as hedging instruments
Fair Values of Derivative Instruments
Fair value of total derivative instruments, Liabilities	103	152
Other accrued expenses and liabilities \| Equity contracts \| Derivative instruments not designated as hedging instruments
Fair Values of Derivative Instruments
Fair value of total derivative instruments, Liabilities	3	7
Other liabilities \| Foreign exchange contracts \| Derivative instruments designated as hedging instruments
Fair Values of Derivative Instruments
Fair value of total derivative instruments, Liabilities	58	78
Long term debt \| Derivative instruments designated as hedging instruments
Fair Values of Derivative Instruments
Fair value of total derivative instruments, Liabilities	1,768	3,035
Short term debt \| Derivative instruments designated as hedging instruments
Fair Values of Derivative Instruments
Fair value of total derivative instruments, Liabilities	$ 1,703	$ 578

This item represents the amount of cash collateral rehypothecated as of the balance sheet date.

No definition available.

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

- Definition

Amount of obligation to return securities collateral under master netting arrangements that have not been offset against derivative assets.

+ References

No definition available.

+ Details

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

- Definition

The credit default swap spread which, if exceeded, would trigger contingent features of these agreements.

+ References

No definition available.

+ Details

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

- Definition

The aggregate fair value of assets that are already posted, at the end of the reporting period, as collateral for derivative instruments with credit-risk-related contingent features.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 133

-Paragraph 44D

-Subparagraph c

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 815

-SubTopic 10

-Section 50

-Paragraph 4H

-Subparagraph (d)

-URI http://asc.fasb.org/extlink&oid=7476318&loc=SL5624258-113959

+ Details

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

- Definition

Fair value of the gross assets less the gross liabilities of a derivative asset or group of derivative assets.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 815

-SubTopic 10

-Section 45

-Paragraph 6

-URI http://asc.fasb.org/extlink&oid=6945355&loc=d3e41271-113958

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 825

-SubTopic 10

-Section 50

-Paragraph 10

-Subparagraph (a)

-URI http://asc.fasb.org/extlink&oid=7491637&loc=d3e13433-108611

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 815

-SubTopic 10

-Section 45

-Paragraph 5

-URI http://asc.fasb.org/extlink&oid=6945355&loc=d3e41228-113958

Reference 4: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 825

-SubTopic 10

-Section 50

-Paragraph 15

-URI http://asc.fasb.org/extlink&oid=7491637&loc=d3e13495-108611

+ Details

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

- Definition

The amount of the obligation to return cash collateral under master netting arrangements that have not been offset against net derivative instrument positions.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 815

-SubTopic 10

-Section 50

-Paragraph 8

-Subparagraph (b)

-URI http://asc.fasb.org/extlink&oid=7476318&loc=d3e41678-113959

+ Details

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

- Definition

The amount of the right to reclaim cash collateral under master netting arrangements that have not been offset against net derivative instrument positions.

+ References

+ Details

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

- Definition

Fair value of derivative asset, presented on a gross basis even when the derivative instrument is subject to master netting arrangements and qualifies for net presentation in the statement of financial position.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 133

-Paragraph 205G

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 133

-Paragraph 44C

-Subparagraph a

-Clause 1

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 815

-SubTopic 10

-Section 50

-Paragraph 4B

-Subparagraph (a),(c)

-URI http://asc.fasb.org/extlink&oid=7476318&loc=SL5624163-113959

+ Details

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

- Definition

Fair value of derivative liability, presented on a gross basis even when the derivative instrument is subject to master netting arrangements and qualifies for net presentation in the statement of financial position.

+ References

+ Details

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

- Definition

+ References

+ Details

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

- Definition

Fair value of the gross liabilities less the gross assets of a derivative liability or group of derivative liabilities.

+ References

+ Details

Name:	us-gaap_DerivativeLiabilityFairValueNet1
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

The aggregate fair value amounts of derivative instruments that contain credit-risk-related contingent features that are in a net liability position at the end of the reporting period. For nonderivative instruments that are designated and qualify as hedging instruments, the fair value amounts are the carrying value of the nonderivative hedging instrument, including the adjustment for the foreign currency transaction gain (loss) on that instrument.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 815

-SubTopic 10

-Section 50

-Paragraph 4H

-Subparagraph (c)

-URI http://asc.fasb.org/extlink&oid=7476318&loc=SL5624258-113959

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 133

-Paragraph 44D

-Subparagraph b

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

+ Details

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

- Details

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

- Details

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