Equity Activity - Reclassifications and Taxes (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2026	Sep. 30, 2025	Sep. 30, 2026	Sep. 30, 2025
Reclassifications and Taxes Related to Items of Other Comprehensive Income
Cost	$ 7,389	$ 6,970	$ 21,611	$ 20,481
SG&A expense	4,620	4,748	14,691	14,661
Other (income) and expense	(109)	(173)	(296)	(376)
Interest expense	491	492	1,451	1,457
Services
Reclassifications and Taxes Related to Items of Other Comprehensive Income
Cost	5,441	5,224	15,979	15,506
Sales
Reclassifications and Taxes Related to Items of Other Comprehensive Income
Cost	1,834	1,637	5,287	4,672
Financing
Reclassifications and Taxes Related to Items of Other Comprehensive Income
Cost	114	109	345	303
Accumulated Other Comprehensive Income/(Loss)
Reclassifications and Taxes Related to Items of Other Comprehensive Income
Other comprehensive income (loss), Before Tax Amount	222	170	1,148	(1,355)
Other comprehensive income/(loss), Tax (Expense)/Benefit	(56)	(112)	(420)	641
Other comprehensive income/(loss)	166	58	728	(715)
Unrealized gains/(losses) arising during the period, Net of Tax Amount			(68)	(572)
Reclassification/amortization, Net of Tax Amount			796	(142)
Foreign currency translation adjustments
Reclassifications and Taxes Related to Items of Other Comprehensive Income
Other comprehensive income (loss), Before Tax Amount	79	(100)	206	(1,056)
Other comprehensive income/(loss), Tax (Expense)/Benefit	(19)	(40)	(177)	562
Other comprehensive income/(loss)	60	(140)	28	(494)
Unrealized gains/(losses) arising during the period, Net of Tax Amount			28	(494)
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	(2)	0	1
Other comprehensive income/(loss), Tax (Expense)/Benefit	0	0	0	0
Other comprehensive income/(loss)	0	(1)	0	0
Unrealized gains/(losses) arising during the period, Net of Tax Amount			0	0
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	(61)	113	321	(769)
Other comprehensive income/(loss), Tax (Expense)/Benefit	18	(30)	(79)	197
Other comprehensive income/(loss)	(43)	84	241	(572)
Unrealized gains/(losses) arising during the period, Before Tax Amount	(66)	20	(123)	(121)
Unrealized gains/(losses) arising during the period, Tax (Expense)/Benefit	18	(6)	28	34
Unrealized gains/(losses) arising during the period, Net of Tax Amount	(48)	14	(94)	(87)
Reclassification/amortization, Net of Tax Amount			336	(485)
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)	(2)	(14)	(3)
Reclassification/amortization, Net of Tax Amount	15	5	43	9
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	0	7	1
Reclassification/amortization, Net of Tax Amount	(7)	0	(12)	(1)
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	3	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)	(4)	(5)
Reclassification/amortization, Net of Tax Amount	4	4	12	13
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	0	2	0
Reclassification/amortization, Net of Tax Amount	(3)	1	(5)	(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	2	(20)	(98)	171
Reclassification/amortization, Net of Tax Amount	(5)	59	295	(508)
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)	1	(7)	(1)
Other (income) and expense	(7)	79	393	(679)
Interest expense	5	6	16	18
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	20	7	57	12
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	(10)	0	(19)	(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	3	3
Total retirement-related benefit plans
Reclassifications and Taxes Related to Items of Other Comprehensive Income
Other comprehensive income (loss), Before Tax Amount	205	158	622	469
Other comprehensive income/(loss), Tax (Expense)/Benefit	(55)	(43)	(163)	(118)
Other comprehensive income/(loss)	150	115	459	351
Unrealized gains/(losses) arising during the period, Net of Tax Amount			(2)	8
Reclassification/amortization, Net of Tax Amount			461	343
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)	26	(5)
Reclassification/amortization, Tax (Expense)/Benefit	(2)	1	(6)	2
Reclassification/amortization, Net of Tax Amount	6	(1)	20	(3)
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	(2)	0	(1)	0
Unrealized gains/(losses) arising during the period, Tax (Expense)/Benefit	0	0	(1)	8
Unrealized gains/(losses) arising during the period, Net of Tax Amount	(2)	0	(2)	8
Reclassification/amortization, Before Tax Amount	196	158	590	466
Reclassification/amortization, Tax (Expense)/Benefit	(52)	(43)	(155)	(126)
Reclassification/amortization, Net of Tax Amount	144	115	436	341
Curtailments and settlements
Reclassifications and Taxes Related to Items of Other Comprehensive Income
Reclassification/amortization, Before Tax Amount	2	2	7	8
Reclassification/amortization, Tax (Expense)/Benefit	0	0	(2)	(2)
Reclassification/amortization, Net of Tax Amount	$ 2	$ 1	$ 5	$ 6