Retirement-Related Benefits - All Retirement Plans Cost (Details) - USD ($) $ in Millions	3 Months Ended
Mar. 31, 2022	Mar. 31, 2021
Retirement-Related Benefits
Defined benefit and contribution pension plans - cost	$ 478	$ 619
Nonpension postretirement plans - cost	33	44
Total	$ 510	$ 663
Year-to-year percent change, defined benefit and contribution pension plans cost (as a percent)	(22.80%)
Year-to-year percent change, nonpension postretirement plans cost (as a percent)	(25.00%)
Year-to-year percent change, total (as a percent)	(23.00%)

The percentage change from year to year in the nonpension postretirement plans cost.

No definition available.

Name:	ibm_OtherPostretirementBenefitExpenseChangePercent
Namespace Prefix:	ibm_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	duration

The percentage change from year to year in the defined benefit and contribution pension plans and the nonpension postretirement plans cost.

No definition available.

Name:	ibm_PensionAndOtherPostretirementBenefitExpenseChangePercent
Namespace Prefix:	ibm_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	duration

The percentage change from year to year in the defined benefit and contribution pension plans cost.

No definition available.

Name:	ibm_PensionExpenseChangePercent
Namespace Prefix:	ibm_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	duration

No definition available.

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

Amount of cost (reversal of cost) for other postretirement benefits. Excludes pension benefits.

No definition available.

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

Amount of cost (reversal of cost) for pension and other postretirement benefits.

No definition available.

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

Amount of cost (reversal of cost) for pension benefits. Excludes other postretirement benefits.

No definition available.