Retirement-Related Benefits - Non-US and Multi-Employer Contributions (Details) - Pension Plans, Including Multi-employer Plans - Non-U.S. - USD ($) $ in Millions	9 Months Ended
Sep. 30, 2018	Sep. 30, 2017
RETIREMENT-RELATED BENEFITS
Expected current year contributions to non-U.S. defined benefit plans	$ 400
Contributions by employer to defined benefit plans	275	$ 301
Contributions by employer - Cash	117	124
Contributions by employer - Noncash	$ 157	$ 176

Cash contributions made by the employer during the period to a defined benefit plan.

No definition available.

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Data Type:	xbrli:monetaryItemType
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- Definition

Noncash contributions made by the employer during the period to a defined benefit plan. These contributions may be in the form of securities.

+ References

No definition available.

+ Details

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Namespace Prefix:	ibm_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
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- Definition

Amount of contribution received by defined benefit plan from employer which increases plan assets.

+ References

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- 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

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- Definition

Amount of contributions received and expected to be received by defined benefit plan from employer in current fiscal year.

+ References

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Balance Type:
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- Details

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