Retirement-Related Benefits (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Retirement-related plans cost:
Total net periodic pension (income)/cost of defined benefit plans	$ (25)	$ (394)	$ (384)
Total retirement-related benefits net periodic cost	1,832	1,382	1,415
Overfunded Plans
Funded status of plan
Benefit Obligations	13,175	72,296
Fair Value of Plan Assets	16,018	75,364
Funded Status	2,843	3,068
Underfunded Plans
Funded status of plan
Benefit Obligations	89,944	27,576
Fair Value of Plan Assets	70,712	10,772
Funded Status	(19,232)	(16,804)
U.S. Plan(s)
Retirement-related plans cost:
Total retirement-related benefits net periodic cost	415	248	358
U.S. Plan(s) \| Underfunded Plans
Funded status of plan
Benefit Obligations	59,358	6,753
Fair Value of Plan Assets	51,256	35
Funded Status	(8,102)	(6,718)
Non-U.S. Plans
Retirement-related plans cost:
Total retirement-related benefits net periodic cost	1,418	1,134	1,057
Non-U.S. Plans \| Overfunded Plans
Funded status of plan
Benefit Obligations	13,175	22,633
Fair Value of Plan Assets	16,018	25,105
Funded Status	2,843	2,472
Non-U.S. Plans \| Underfunded Plans
Funded status of plan
Benefit Obligations	30,587	20,823
Fair Value of Plan Assets	19,456	10,737
Funded Status	(11,131)	(10,086)
Defined Benefit Pension Plans
Retirement-related plans cost:
Total net periodic pension (income)/cost of defined benefit plans	(40)	(408)	(398)
Funded status of plan
Percentage of funded status (as a percent)	89.00%
Defined Benefit Pension Plans \| U.S. Plan(s)
Retirement-related plans cost:
Total net periodic pension (income)/cost of defined benefit plans	(759)	(935)	(906)
Funded status of plan
Benefit Obligations	54,085	51,293	48,354
Fair Value of Plan Assets	51,218	50,259	47,269
Funded Status	(2,866)	(1,034)
Defined Benefit Pension Plans \| Non-U.S. Plans
Retirement-related plans cost:
Total net periodic pension (income)/cost of defined benefit plans	734	541	521
Funded status of plan
Benefit Obligations	42,861	42,584	41,308
Fair Value of Plan Assets	35,362	35,722	34,305
Funded Status	(7,499)	(6,861)
Personal Pension Plan (PPP)
Period used in determining benefits (in years)	5 years
Personal Pension Plan (PPP) \| U.S. Plan(s)
Retirement-related plans cost:
Total net periodic pension (income)/cost of defined benefit plans	(774)	(949)	(919)
Qualified PPP (Qualified defined benefit pension plans)
Funded status of plan
Percentage of funded status (as a percent)	96.00%
Qualified PPP (Qualified defined benefit pension plans) \| U.S. Plan(s)
Funded status of plan
Fair Value of Plan Assets	51,218	50,259
Percentage of funded status (as a percent)	98.00%
Qualified PPP (Qualified defined benefit pension plans) \| U.S. Plan(s) \| Overfunded Plans
Funded status of plan
Benefit Obligations		49,663
Fair Value of Plan Assets		50,259
Funded Status		596
Qualified PPP (Qualified defined benefit pension plans) \| U.S. Plan(s) \| Underfunded Plans
Funded status of plan
Benefit Obligations	52,318
Fair Value of Plan Assets	51,218
Funded Status	(1,100)
Excess PPP (Nonqualified defined benefit pension plans) \| U.S. Plan(s) \| Underfunded Plans
Funded status of plan
Benefit Obligations	1,462	1,360
Funded Status	(1,462)	(1,360)
Retention Plan
Retirement-related plans cost:
Total net periodic pension (income)/cost of defined benefit plans	15	14	13
Retention Plan \| U.S. Plan(s)
Retirement-related plans cost:
Total net periodic pension (income)/cost of defined benefit plans	15	14	13
Retention Plan \| U.S. Plan(s) \| Underfunded Plans
Funded status of plan
Benefit Obligations	305	271
Funded Status	(305)	(271)
Non-US Defined Benefit Pension Plans \| Non-U.S. Plans
Retirement-related plans cost:
Total net periodic pension (income)/cost of defined benefit plans	734	541	521
Qualified defined benefit pension plans \| Non-U.S. Plans \| Overfunded Plans
Funded status of plan
Benefit Obligations	13,169	22,625
Fair Value of Plan Assets	16,011	25,096
Funded Status	2,843	2,471
Qualified defined benefit pension plans \| Non-U.S. Plans \| Underfunded Plans
Funded status of plan
Benefit Obligations	24,659	14,507
Fair Value of Plan Assets	19,351	10,626
Funded Status	(5,308)	(3,881)
Nonqualified defined benefit pension plans \| Non-U.S. Plans \| Underfunded Plans
Funded status of plan
Benefit Obligations	5,033	5,452
Funded Status	(5,033)	(5,452)
Defined Contribution Plans
Retirement-related plans cost:
Cost of defined contribution plans	1,513	1,430	1,450
Defined Contribution Plans \| U.S. Plan(s)
Retirement-related plans cost:
Cost of defined contribution plans	905	902	972
Defined Contribution Plans \| Non-U.S. Plans
Retirement-related plans cost:
Cost of defined contribution plans	608	527	478
IBM 401(k) Plus Plan
Defined Contribution Plans
Maximum percentage, dollar-for-dollar match by entity to employee contribution of eligible compensation for employees hired prior to January 1, 2005 (as a percent)	6.00%	6.00%
Maximum percentage, dollar-for-dollar match by entity to employee contribution of eligible compensation for employees hired after January 1, 2005 (as a percent)	5.00%	5.00%
Employer's automatic contribution as a percentage of eligible compensation, lowest level defined	1.00%	1.00%
Employer's automatic contribution as a percentage of eligible compensation, second level defined	2.00%	2.00%
Employer's automatic contribution as a percentage of eligible compensation, highest level defined	4.00%	4.00%
Service period after which employees receive automatic contributions (in years)	1 year	1 year
Retirement-related plans cost:
Cost of defined contribution plans	1,483	1,409	1,424
IBM 401(k) Plus Plan \| U.S. Plan(s)
Retirement-related plans cost:
Cost of defined contribution plans	875	882	946
IBM Excess 401(k) Plus Plan
Defined Contribution Plans
Service period after which employees receive automatic contributions (in years)	1 year	1 year
Retirement-related plans cost:
Cost of defined contribution plans	30	20	26
IBM Excess 401(k) Plus Plan \| U.S. Plan(s)
Retirement-related plans cost:
Cost of defined contribution plans	30	20	26
Other defined contribution plans \| Non-U.S. Plans
Retirement-related plans cost:
Cost of defined contribution plans	608	527	478
Nonpension Postretirement Plans
Retirement-related plans cost:
Total net periodic pension (income)/cost of defined benefit plans	345	347	350
Nonpension Postretirement Plans \| U.S. Plan(s)
Retirement-related plans cost:
Minimum years of service remaining from retirement eligibility to participate in Future Health Account (FHA) benefits	5 years	5 years
Service period for retirement within which employees are covered under the entity's prior health benefits arrangements (in years)	5 years	5 years
Total net periodic pension (income)/cost of defined benefit plans	269	281	292
Funded status of plan
Benefit Obligations	5,273	5,123	5,100
Fair Value of Plan Assets	38	35	33
Funded Status	(5,235)	(5,088)
Nonpension Postretirement Plans \| U.S. Plan(s) \| Underfunded Plans
Funded status of plan
Benefit Obligations	5,273	5,123
Fair Value of Plan Assets	38	35
Funded Status	(5,235)	(5,088)
Nonpension Postretirement Plans \| Non-U.S. Plans
Retirement-related plans cost:
Total net periodic pension (income)/cost of defined benefit plans	76	66	58
Funded status of plan
Benefit Obligations	901	872	767
Fair Value of Plan Assets	112	120	104
Funded Status	(789)	(752)
Nonpension Postretirement Plans \| Non-U.S. Plans \| Overfunded Plans
Funded status of plan
Benefit Obligations	7	8
Fair Value of Plan Assets	7	9
Funded Status	0	1
Nonpension Postretirement Plans \| Non-U.S. Plans \| Underfunded Plans
Funded status of plan
Benefit Obligations	894	864
Fair Value of Plan Assets	105	111
Funded Status	$ (789)	$ (753)

Name:	ibm_DefinedBenefitPlanDisclosureAbstract
Namespace Prefix:	ibm_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

The percentage of funded status of the plan.

+ References

No definition available.

+ Details

Name:	ibm_DefinedBenefitPlanPercentageOfFundedStatusOfPlan
Namespace Prefix:	ibm_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Represents the employer's contribution expressed as a percentage of eligible compensation under condition one depending on the employee's eligibility to participate in the PPP as on December 31, 2007.

+ References

No definition available.

+ Details

Name:	ibm_EmployerContributionAsPercentageOfEligibleCompensationUnderConditionOne
Namespace Prefix:	ibm_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Represents the employer's contribution expressed as a percentage of eligible compensation under condition three depending on the employees' eligibility to participate in the PPP as on December 31, 2007.

+ References

No definition available.

+ Details

Name:	ibm_EmployerContributionAsPercentageOfEligibleCompensationUnderConditionThree
Namespace Prefix:	ibm_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Represents the employer's contribution expressed as a percentage of eligible compensation under condition two depending on the employees' eligibility to participate in the PPP as on December 31, 2007.

+ References

No definition available.

+ Details

Name:	ibm_EmployerContributionAsPercentageOfEligibleCompensationUnderConditionTwo
Namespace Prefix:	ibm_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

This element represents minimum years of service remaining from retirement eligibility to participate in Future Health Account benefits.

+ References

No definition available.

+ Details

Name:	ibm_MinimumNumberOfYearsOfServiceRemainingForRetirementToBeEligibleForFutureHealthAccountBenefits
Namespace Prefix:	ibm_
Data Type:	us-types:durationStringItemType
Balance Type:	na
Period Type:	duration

- Definition

The service period after which employees receive automatic contributions and matching contributions.

+ References

No definition available.

+ Details

Name:	ibm_MinimumServicePeriodAfterWhichEmployeesAreEligibleToReceiveContributions
Namespace Prefix:	ibm_
Data Type:	us-types:durationStringItemType
Balance Type:	na
Period Type:	duration

- Definition

This element represents maximum percentage of dollar-for-dollar match of employees contribution for those hired after January 1, 2005.

+ References

No definition available.

+ Details

Name:	ibm_PercentageOfEmployeeContributionOnEligibleCompensationForEmployeesHiredPost1stJanuary2005
Namespace Prefix:	ibm_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

This element represents maximum percentage of dollar-for-dollar match of employees contribution for those hired prior to January 1, 2005.

+ References

No definition available.

+ Details

Name:	ibm_PercentageOfEmployeeContributionOnEligibleCompensationForEmployeesHiredPrior1stJanuary2005
Namespace Prefix:	ibm_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

This element represents the period, which is used in the computation of benefits based on salary, years of service, mortality and other participant-specific factors using final pay formula.

+ References

No definition available.

+ Details

Name:	ibm_PeriodUsedToDetermineBenefitsUsingFinalPayFormula
Namespace Prefix:	ibm_
Data Type:	us-types:durationStringItemType
Balance Type:	na
Period Type:	duration

- Definition

Employees who were within the specified period of retirement eligibility are covered under the company's prior retiree health benefits arrangements.

+ References

No definition available.

+ Details

Name:	ibm_ServicePeriodWithinTheSpecifiedYearsOfRetirementCoveredUnderRetireeHealthBenefitsArrangements
Namespace Prefix:	ibm_
Data Type:	us-types:durationStringItemType
Balance Type:	na
Period Type:	duration

- Definition

1) For defined benefit pension plans, the benefit obligation is the projected benefit obligation, which is the actuarial present value as of a date of all benefits attributed by the pension benefit formula to employee service rendered prior to that date. 2) For other postretirement defined benefit plans, the benefit obligation is the accumulated postretirement benefit obligation, which is the actuarial present value of benefits attributed to employee service rendered to a particular date.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Glossary Projected Benefit Obligation

-URI http://asc.fasb.org/extlink&oid=6522206

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

-Publisher FASB

-Name Accounting Standards Codification

-Glossary Accumulated Postretirement Benefit Obligation

-URI http://asc.fasb.org/extlink&oid=6503904

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

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 132R

-Paragraph 5

-Subparagraph a

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 715

-SubTopic 20

-Section 50

-Paragraph 1

-Subparagraph (a)

-URI http://asc.fasb.org/extlink&oid=6962843&loc=d3e1928-114920

Reference 5: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 132R

-Paragraph 6

-Subparagraph a

-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 6: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 132R

-Paragraph E1

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

- Definition

Assets, usually stocks, bonds, and other investments, that have been segregated and restricted (usually in a trust) to provide benefits, at their fair value as of the measurement date. Plan assets include amounts contributed by the employer (and by employees for a contributory plan) and amounts earned from investing the contributions, less benefits paid. If a plan has liabilities other than for benefits, those non-benefit obligations may be considered as reductions of plan assets.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 715

-SubTopic 30

-Section 35

-Paragraph 50

-URI http://asc.fasb.org/extlink&oid=6867990&loc=d3e12355-114930

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

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 132R

-Paragraph 5

-Subparagraph d(iv)(b)(i)

-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 Statement of Financial Accounting Standard (FAS)

-Number 132R

-Paragraph 5

-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.

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

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 87

-Paragraph 49

-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 5: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 715

-SubTopic 20

-Section 50

-Paragraph 1

-Subparagraph (b)

-URI http://asc.fasb.org/extlink&oid=6962843&loc=d3e1928-114920

+ Details

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

- Definition

The funded status is measured as the difference between the fair value of plan assets and the benefit obligation. Will normally be the same as the net Defined Benefit Plan, Amounts Recognized in Balance Sheet, Total.

+ References

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

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 132R

-Paragraph 5

-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 715

-SubTopic 20

-Section 45

-Paragraph 2

-URI http://asc.fasb.org/extlink&oid=6410544&loc=d3e1703-114919

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 715

-SubTopic 20

-Section 50

-Paragraph 1

-Subparagraph (c)

-URI http://asc.fasb.org/extlink&oid=6962843&loc=d3e1928-114920

+ Details

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

- Details

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

- Definition

The total amount of net periodic benefit cost for defined benefit plans for the period. Periodic benefit costs include the following components: service cost, interest cost, expected return on plan assets, gain (loss), prior service cost or credit, transition asset or obligation, and gain (loss) due to settlements or curtailments.

+ References

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

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 132R

-Paragraph 5

-Subparagraph h

-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 715

-SubTopic 20

-Section 50

-Paragraph 1

-Subparagraph (h)

-URI http://asc.fasb.org/extlink&oid=6962843&loc=d3e1928-114920

+ Details

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

- Details

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

- Definition

The amount of the cost recognized during the period for defined contribution plans.

+ References

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

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 132R

-Paragraph 11

-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 715

-SubTopic 70

-Section 50

-Paragraph 1

-URI http://asc.fasb.org/extlink&oid=6414718&loc=d3e28014-114942

+ Details

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

- Definition

The amount of pension and other (such as medical, dental and life insurance) postretirement benefit costs recognized during the period for (1) defined benefit plans (periodic benefit costs include the following components: service cost, interest cost, expected return on plan assets, gain (loss) on assets, prior service cost or credit, transition asset or obligation, and gain (loss) due to settlements or curtailments) and for (2) defined contribution plans (to the extent that a plan's defined contributions to an individual's account are to be made for periods in which that individual renders services, the net cost for a period is the contribution called for in that period; if a plan calls for contributions for periods after an individual retires or terminates, the estimated cost is accrued during the employee's service period).

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 230

-SubTopic 10

-Section 45

-Paragraph 28

-URI http://asc.fasb.org/extlink&oid=6943989&loc=d3e3602-108585

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 225

-SubTopic 10

-Section S99

-Paragraph 2

-Subparagraph (SX 210.5-03.4)

-URI http://asc.fasb.org/extlink&oid=6880815&loc=d3e20235-122688

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

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 95

-Paragraph 28

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 715

-SubTopic 70

-Section 50

-Paragraph 1

-URI http://asc.fasb.org/extlink&oid=6414718&loc=d3e28014-114942

Reference 5: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 132R

-Paragraph 5

-Subparagraph h

-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 6: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 132R

-Paragraph 5, 11

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