Equity Activity - Reclassifications and Taxes (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2026	Jun. 30, 2025	Jun. 30, 2026	Jun. 30, 2025
Reclassifications and Taxes Related to Items of Other Comprehensive Income
Cost	$ 7,255	$ 7,001	$ 14,222	$ 13,511
SG&A expense	4,981	5,027	10,071	9,913
Other (income) and expense	(185)	(39)	(186)	(204)
Interest expense	486	510	959	965
Services
Reclassifications and Taxes Related to Items of Other Comprehensive Income
Cost	5,294	5,280	10,538	10,282
Sales
Reclassifications and Taxes Related to Items of Other Comprehensive Income
Cost	1,854	1,630	3,453	3,034
Financing
Reclassifications and Taxes Related to Items of Other Comprehensive Income
Cost	107	90	232	194
Accumulated Other Comprehensive Income/(Loss)
Reclassifications and Taxes Related to Items of Other Comprehensive Income
Other comprehensive income (loss), Before Tax Amount	414	(959)	926	(1,525)
Other comprehensive income/(loss), Tax (Expense)/Benefit	(150)	493	(364)	753
Other comprehensive income/(loss)	263	(466)	562	(772)
Unrealized gains/(losses) arising during the period, Net of Tax Amount			(77)	(445)
Reclassification/amortization, Net of Tax Amount			639	(328)
Foreign currency translation adjustments
Reclassifications and Taxes Related to Items of Other Comprehensive Income
Other comprehensive income (loss), Before Tax Amount	(9)	(613)	127	(956)
Other comprehensive income/(loss), Tax (Expense)/Benefit	(42)	399	(158)	602
Other comprehensive income/(loss)	(51)	(215)	(31)	(354)
Unrealized gains/(losses) arising during the period, Net of Tax Amount			(31)	(354)
Reclassification/amortization, Net of Tax Amount			0	0
Net unrealized gains/(losses) on available-for-sale securities
Reclassifications and Taxes Related to Items of Other Comprehensive Income
Other comprehensive income (loss), Before Tax Amount	0	(5)	0	2
Other comprehensive income/(loss), Tax (Expense)/Benefit	0	1	0	(1)
Other comprehensive income/(loss)	0	(4)	0	2
Unrealized gains/(losses) arising during the period, Net of Tax Amount			0	2
Reclassification/amortization, Net of Tax Amount			0	0
Net Unrealized Gains/(Losses) on Cash Flow Hedges
Reclassifications and Taxes Related to Items of Other Comprehensive Income
Other comprehensive income (loss), Before Tax Amount	215	(501)	382	(883)
Other comprehensive income/(loss), Tax (Expense)/Benefit	(54)	128	(97)	227
Other comprehensive income/(loss)	161	(373)	285	(656)
Unrealized gains/(losses) arising during the period, Before Tax Amount	119	(82)	(56)	(141)
Unrealized gains/(losses) arising during the period, Tax (Expense)/Benefit	(31)	24	10	40
Unrealized gains/(losses) arising during the period, Net of Tax Amount	87	(59)	(46)	(101)
Reclassification/amortization, Net of Tax Amount			331	(555)
Net Unrealized Gains/(Losses) on Cash Flow Hedges | Income Statement Location [Axis]: us-gaap:CostOfRevenue | Services
Reclassifications and Taxes Related to Items of Other Comprehensive Income
Reclassification/amortization, Tax (Expense)/Benefit	(5)	(1)	(9)	(1)
Reclassification/amortization, Net of Tax Amount	17	3	28	4
Net Unrealized Gains/(Losses) on Cash Flow Hedges | Income Statement Location [Axis]: us-gaap:CostOfRevenue | Sales
Reclassifications and Taxes Related to Items of Other Comprehensive Income
Reclassification/amortization, Tax (Expense)/Benefit	3	(2)	4	1
Reclassification/amortization, Net of Tax Amount	(6)	4	(6)	(2)
Net Unrealized Gains/(Losses) on Cash Flow Hedges | Income Statement Location [Axis]: us-gaap:CostOfRevenue | Financing
Reclassifications and Taxes Related to Items of Other Comprehensive Income
Reclassification/amortization, Tax (Expense)/Benefit	0	0	(1)	(1)
Reclassification/amortization, Net of Tax Amount	1	1	2	2
Net Unrealized Gains/(Losses) on Cash Flow Hedges | Income Statement Location [Axis]: us-gaap:InterestExpense
Reclassifications and Taxes Related to Items of Other Comprehensive Income
Reclassification/amortization, Tax (Expense)/Benefit	(1)	(1)	(3)	(3)
Reclassification/amortization, Net of Tax Amount	4	4	8	9
Net Unrealized Gains/(Losses) on Cash Flow Hedges | Income Statement Location [Axis]: us-gaap:SellingGeneralAndAdministrativeExpense
Reclassifications and Taxes Related to Items of Other Comprehensive Income
Reclassification/amortization, Tax (Expense)/Benefit	1	(1)	1	0
Reclassification/amortization, Net of Tax Amount	(3)	1	(2)	(1)
Net Unrealized Gains/(Losses) on Cash Flow Hedges | Income Statement Location [Axis]: ibm:OtherExpenseAndIncome
Reclassifications and Taxes Related to Items of Other Comprehensive Income
Reclassification/amortization, Tax (Expense)/Benefit	(20)	110	(100)	191
Reclassification/amortization, Net of Tax Amount	60	(327)	300	(567)
Net Unrealized Gains/(Losses) on Cash Flow Hedges | Reclassification out of Accumulated Other Comprehensive Income
Reclassifications and Taxes Related to Items of Other Comprehensive Income
SG&A expense	(4)	2	(3)	(2)
Other (income) and expense	80	(436)	400	(758)
Interest expense	5	6	11	12
Net Unrealized Gains/(Losses) on Cash Flow Hedges | Reclassification out of Accumulated Other Comprehensive Income | Services
Reclassifications and Taxes Related to Items of Other Comprehensive Income
Cost	22	4	37	5
Net Unrealized Gains/(Losses) on Cash Flow Hedges | Reclassification out of Accumulated Other Comprehensive Income | Sales
Reclassifications and Taxes Related to Items of Other Comprehensive Income
Cost	(8)	5	(9)	(2)
Net Unrealized Gains/(Losses) on Cash Flow Hedges | Reclassification out of Accumulated Other Comprehensive Income | Financing
Reclassifications and Taxes Related to Items of Other Comprehensive Income
Cost	1	1	2	2
Total retirement-related benefit plans
Reclassifications and Taxes Related to Items of Other Comprehensive Income
Other comprehensive income (loss), Before Tax Amount	208	160	417	311
Other comprehensive income/(loss), Tax (Expense)/Benefit	(54)	(35)	(109)	(76)
Other comprehensive income/(loss)	154	125	309	236
Unrealized gains/(losses) arising during the period, Net of Tax Amount			1	8
Reclassification/amortization, Net of Tax Amount			308	228
Prior service costs/(credits)
Reclassifications and Taxes Related to Items of Other Comprehensive Income
Unrealized gains/(losses) arising during the period, Before Tax Amount	0	0	0	0
Unrealized gains/(losses) arising during the period, Tax (Expense)/Benefit	0	0	0	0
Unrealized gains/(losses) arising during the period, Net of Tax Amount	0	0	0	0
Reclassification/amortization, Before Tax Amount	9	(2)	18	(4)
Reclassification/amortization, Tax (Expense)/Benefit	(2)	1	(4)	1
Reclassification/amortization, Net of Tax Amount	7	(1)	13	(2)
Net gains/(losses) arising during the period
Reclassifications and Taxes Related to Items of Other Comprehensive Income
Unrealized gains/(losses) arising during the period, Before Tax Amount	0	0	1	0
Unrealized gains/(losses) arising during the period, Tax (Expense)/Benefit	0	8	0	8
Unrealized gains/(losses) arising during the period, Net of Tax Amount	0	8	1	8
Reclassification/amortization, Before Tax Amount	197	157	394	308
Reclassification/amortization, Tax (Expense)/Benefit	(51)	(42)	(103)	(83)
Reclassification/amortization, Net of Tax Amount	145	115	291	225
Curtailments and settlements
Reclassifications and Taxes Related to Items of Other Comprehensive Income
Reclassification/amortization, Before Tax Amount	3	5	4	7
Reclassification/amortization, Tax (Expense)/Benefit	(1)	(2)	(1)	(2)
Reclassification/amortization, Net of Tax Amount	$ 2	$ 3	$ 3	$ 5