The amount of pension funds allocated to portfolio, which are available for future investments.

No definition available.

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

- Definition

An assumption as to the rate of return on plan assets for the next year reflecting the average rate of earnings expected on the funds invested or to be invested to provide for the benefits included in the benefit obligation.

+ References

No definition available.

+ Details

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

- Definition

The net increase or decrease in the accumulated plan benefit obligation, during the reporting period, on account of changes in discount rate assumptions.

+ References

No definition available.

+ Details

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

- Definition

The net increase or decrease in the plan benefit obligation, during the reporting period, on account of changes in discount rate assumptions.

+ References

No definition available.

+ Details

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

- Definition

The increase (decrease) in the net periodic income (cost), due to changes in discount rate assumptions.

+ References

No definition available.

+ Details

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

- Definition

The increase (decrease) in the net periodic income (cost), due to changes in expected long-term rate of return on plan assets.

+ References

No definition available.

+ Details

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

- Definition

The increase (decrease) in net periodic (income) cost due to change in interest crediting rate.

+ References

No definition available.

+ Details

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

- Definition

The net increase/(decrease) in the plan benefit obligation, during the reporting period, on account of changes in mortality rate assumptions.

+ References

No definition available.

+ Details

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

- Definition

This element represents the interest crediting rate.

+ References

No definition available.

+ Details

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

- Details

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

- Details

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

- Details

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

- Definition

This element represents the number of years over which changes in the fair value of plan assets in the expected return on plan assets line in net periodic (Income)/cost is systematically recognized.

+ References

No definition available.

+ Details

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

- Definition

The percentage of board members, elected by employees and retirees for managing investments.

+ References

No definition available.

+ Details

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

- Definition

This element represents percentage of interest rate added to average from August to October of the one-year U.S. Treasury Constant Maturity yield for computation of interest crediting rate.

+ References

No definition available.

+ Details

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

- Details

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

- Details

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

- Definition

The interest rate used to adjust for the time value of money for the plan.

+ References

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Expected rate of compensation increases (for pay-related plans).

+ References

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

The interest rate used to adjust for the time value of money.

+ References

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

An assumption as to the rate of return on plan assets reflecting the average rate of earnings expected on the funds invested or to be invested to provide for the benefits included in the benefit obligation.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 715

-SubTopic 30

-Glossary Expected Long-Term Rate of Return on Plan Assets

-URI http://asc.fasb.org/extlink&oid=6512013

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 715

-SubTopic 20

-Section 50

-Paragraph 1

-Subparagraph (k)(3)

-URI http://asc.fasb.org/extlink&oid=35743120&loc=d3e1928-114920

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Expected rate of compensation increases (for pay-related plans).

+ References

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount of effect of a one-percentage-point decrease in the assumed health care cost trend rates on the accumulated postretirement benefit obligation for health care benefits.

+ References

+ Details

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

- Definition

Amount of effect of a one-percentage-point decrease in the assumed health care cost trend rates on the aggregate of the service and interest cost components of net periodic postretirement health care benefit costs.

+ References

+ Details

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Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

The effect of a one-percentage-point increase in the assumed health care cost trend rates on the accumulated postretirement benefit obligation for health care benefits.

+ References

+ Details

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Namespace Prefix:	us-gaap_
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Period Type:	duration

- Definition

The effect of a one-percentage-point increase in the assumed health care cost trend rates on the aggregate of the service and interest cost components of net periodic postretirement health care benefit costs.

+ References

+ Details

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Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- 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 20

-Section 50

-Paragraph 1

-Subparagraph (b)

-URI http://asc.fasb.org/extlink&oid=35743120&loc=d3e1928-114920

Reference 2: 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=29635418&loc=d3e12355-114930

+ Details

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

- Definition

The assumed health care cost trend rate for the next year used to measure the expected cost of benefits covered by the plan (gross eligible charges). This is based upon the annual rate of change in the cost of health care benefits currently provided by the postretirement benefit plan, due to factors other than changes in the composition of the plan population by age and dependency status.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 715

-SubTopic 20

-Section 50

-Paragraph 1

-Subparagraph (l)

-URI http://asc.fasb.org/extlink&oid=35743120&loc=d3e1928-114920

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

-Publisher FASB

-Name Accounting Standards Codification

-Glossary Health Care Cost Trend Rate

-URI http://asc.fasb.org/extlink&oid=6514820

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Target allocation of investments of this type to total plan assets presented on a weighted average basis.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 715

-SubTopic 20

-Section 50

-Paragraph 1

-Subparagraph (d)(i)

-URI http://asc.fasb.org/extlink&oid=35743120&loc=d3e1928-114920

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 715

-SubTopic 20

-Section 50

-Paragraph 5

-Subparagraph (c)(i)

-URI http://asc.fasb.org/extlink&oid=35743120&loc=d3e2446-114920

+ Details

Name:	us-gaap_DefinedBenefitPlanTargetPlanAssetAllocations
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

The ultimate trend rate for health care costs.

+ References

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
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Period Type:	duration

- Details

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Period Type:	duration

- Definition

Year the ultimate health care cost trend rate is expected to be reached, in CCYY format.

+ References

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:gYearItemType
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Period Type:	instant

- Details

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Retirement-Related Benefits (Assumptions) (Details 8) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Defined Benefit Pension Plans
Expected Long-Term Returns on Plan Assets
Period over which changes in fair value of plan assets recognized	5 years
U.S. Defined Benefit Pension Plans
Weighted-average assumptions used to measure net periodic (income)/cost for the year ended December 31
Discount rate	4.50%	3.60%	4.20%
Expected long-term returns on plan assets	8.00%	8.00%	8.00%
Weighted-average assumptions used to measure benefit obligations at December 31
Discount rate	3.70%	4.50%	3.60%
Discount Rate
Increase (decrease) in net periodic (income) cost due to change in discount rate	$ 275	$ (162)	$ (258)
Increase (decrease) in retirement related benefit plan obligation due to change in discount rate	4,437	(4,785)
Investment Policies And Strategies
Fair Value of plan assets	55,772	53,954	53,630
Personal Pension Plan (PPP)
Interest Crediting Rate
Percentage interest rate added to average interest from August to October of the one-year U.S Treasury Constant Maturity yield for computation of interest crediting rate (as a percent)	1.00%
Interest crediting rate	1.10%	1.20%	1.10%	1.30%
Increase (decrease) in net periodic (income) cost due to change in interest crediting rate	8	(6)	10
Qualified PPP
Weighted-average assumptions used to measure net periodic (income)/cost for the year ended December 31
Expected long-term returns on plan assets	8.00%	8.00%	8.00%
Projected long-term rate of return on plan assets for the next fiscal year	7.50%
Expected Long-Term Returns on Plan Assets
Increase (decrease) in net periodic (income) cost due to change in expected long-term rate of return on plan assets	0	0	0
Investment Policies And Strategies
Fair Value of plan assets	55,772	53,954
Qualified PPP \| Equity securities
Investment Policies And Strategies
Target allocation	33.00%
Qualified PPP \| Fixed income
Investment Policies And Strategies
Target allocation	57.00%
Qualified PPP \| Real estate
Investment Policies And Strategies
Target allocation	5.00%
Qualified PPP \| Other investments
Investment Policies And Strategies
Target allocation	5.00%
Qualified PPP \| Private equities and private real estate investments
Investment Policies And Strategies
Commitments for future investments in private markets	2,629
Fair Value of plan assets	6,229
Non-U.S. Defined Benefit Pension Plans
Weighted-average assumptions used to measure net periodic (income)/cost for the year ended December 31
Discount rate	3.32%	3.23%	4.28%
Expected long-term returns on plan assets	6.08%	6.21%	6.26%
Rate of compensation increase	2.52%	2.51%	2.43%
Weighted-average assumptions used to measure benefit obligations at December 31
Discount rate	2.34%	3.32%	3.23%
Rate of compensation increase	2.49%	2.52%	2.51%
Investment Policies And Strategies
Fair Value of plan assets	39,543	39,464	38,058
Non-U.S. Defined Benefit Pension Plans \| Maximum
Investment Policies And Strategies
Percentage of board members, elected by employees and retirees for managing investments (as a percent)	50.00%
Non-U.S. Defined Benefit Pension Plans \| Equity securities
Investment Policies And Strategies
Target allocation	32.00%
Non-U.S. Defined Benefit Pension Plans \| Fixed income
Investment Policies And Strategies
Target allocation	56.00%
Non-U.S. Defined Benefit Pension Plans \| Real estate
Investment Policies And Strategies
Target allocation	2.00%
Non-U.S. Defined Benefit Pension Plans \| Other investments
Investment Policies And Strategies
Target allocation	10.00%
Nonpension Postretirement Plans
Weighted-average assumptions used to measure net periodic (income)/cost for the year ended December 31
Expected long-term returns on plan assets	0.00%	0.00%	0.00%
Healthcare Cost Trend Rate
Health care cost trend rate assumed for next fiscal year	7.00%
Ultimate healthcare cost trend rate	5.00%
Year that rate reaches ultimate trend rate	2019
Effect of one percentage point increase on net periodic cost	0	0	0
Effect of one percentage point decrease on net periodic cost	0	0	0
Effect of one percentage point increase on benefit obligation	0	0
Effect of one percentage point decrease on benefit obligation	0	0
U.S. Nonpension Postretirement Benefit Plans
Weighted-average assumptions used to measure net periodic (income)/cost for the year ended December 31
Discount rate	4.10%	3.30%	3.90%
Expected long-term returns on plan assets		0.35%
Weighted-average assumptions used to measure benefit obligations at December 31
Discount rate	3.40%	4.10%	3.30%
Discount Rate
Increase (decrease) in net periodic (income) cost due to change in discount rate	0	0	0
Increase (decrease) in APBO due to changes in discount rate	256	(298)
Investment Policies And Strategies
Fair Value of plan assets	16	177	433
Non-U.S. Nonpension Postretirement Plans
Weighted-average assumptions used to measure net periodic (income)/cost for the year ended December 31
Discount rate	7.78%	6.43%	7.37%
Expected long-term returns on plan assets	10.22%	9.01%	9.01%
Weighted-average assumptions used to measure benefit obligations at December 31
Discount rate	7.51%	7.78%	6.43%
Investment Policies And Strategies
Fair Value of plan assets	84	92	119
Retirement-related benefit plans
Discount Rate
Increase (decrease) in retirement related benefit plan obligation due to change in discount rate	11,000
U.S. Retirement-related benefit plans
Discount Rate
Increase (decrease) in benefit obligations due to change in mortality rate assumptions	$ 2,600