Derivative Financial Instruments - Gains and Losses (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2026	Sep. 30, 2025	Sep. 30, 2026	Sep. 30, 2025
Derivative Instruments, Gain (Loss)
Derivative, Gain (Loss), Statement of Income or Comprehensive Income [Extensible Enumeration]	Cost, Interest expense, Selling, general and administrative, Other (income) and expense	Cost, Interest expense, Selling, general and administrative, Other (income) and expense	Cost, Interest expense, Selling, general and administrative, Other (income) and expense	Cost, Interest expense, Selling, general and administrative, Other (income) and expense
(Gains)/losses recognized on derivatives	$ 194	$ 0	$ 316	$ (451)
(Gains)/losses recognized in earnings attributable to risk being hedged	(114)	27	(173)	146
(Gains)/Losses Recognized in Earnings and Other Comprehensive Income - Recognized in OCI	11	179	588	(2,356)
(Gains)/Losses Recognized in Earnings and Other Comprehensive Income - Reclassified from AOCI	(32)	66	338	(732)
(Gains)/Losses Recognized in Earnings and Other Comprehensive Income - Amounts Excluded from Effectiveness Testing	19	(4)	47	(1)
Interest rate contracts | Cash Flow Hedging
Derivative Instruments, Gain (Loss)
(Gains)/Losses Recognized in Earnings and Other Comprehensive Income - Recognized in OCI - Cash flow hedges	0	0	0	0
Foreign exchange contracts | Not Designated as Hedging Instrument, Economic Hedge
Derivative Instruments, Gain (Loss)
(Gains)/losses recognized on derivatives	28	83	167	(202)
Foreign exchange contracts | Cash Flow Hedging
Derivative Instruments, Gain (Loss)
(Gains)/Losses Recognized in Earnings and Other Comprehensive Income - Recognized in OCI - Cash flow hedges	(42)	70	(103)	87
(Gains)/Losses Recognized in Earnings and Other Comprehensive Income - Recognized in OCI - Amount excluded from the assessment of effectiveness	(24)	(50)	(20)	(207)
(Gains)/Losses Recognized in Earnings and Other Comprehensive Income - Amounts Excluded from Effectiveness Testing	37	28	105	84
Foreign exchange contracts | Net Investment Hedging
Derivative Instruments, Gain (Loss)
(Gains)/Losses Recognized in Earnings and Other Comprehensive Income - Recognized in OCI - Amount excluded from the assessment of effectiveness	(6)	6	(22)	17
(Gains)/Losses Recognized in Earnings and Other Comprehensive Income - Recognized in OCI - Net investment hedges	83	154	733	(2,252)
Equity contracts | Not Designated as Hedging Instrument, Economic Hedge
Derivative Instruments, Gain (Loss)
(Gains)/losses recognized on derivatives	42	(75)	(53)	(156)
Income Statement Location [Axis]: us-gaap:CostOfRevenue | Interest rate contracts | Fair Value Hedging
Derivative Instruments, Gain (Loss)
(Gains)/losses recognized on derivatives	22	(1)	36	(14)
(Gains)/losses recognized in earnings attributable to risk being hedged	(20)	4	(31)	23
Income Statement Location [Axis]: us-gaap:CostOfRevenue | Interest rate contracts | Cash Flow Hedging
Derivative Instruments, Gain (Loss)
(Gains)/Losses Recognized in Earnings and Other Comprehensive Income - Reclassified from AOCI	0	1	2	2
Income Statement Location [Axis]: us-gaap:CostOfRevenue | Foreign exchange contracts | Cash Flow Hedging | Services
Derivative Instruments, Gain (Loss)
(Gains)/Losses Recognized in Earnings and Other Comprehensive Income - Reclassified from AOCI	20	7	57	12
Income Statement Location [Axis]: us-gaap:CostOfRevenue | Foreign exchange contracts | Cash Flow Hedging | Sales
Derivative Instruments, Gain (Loss)
(Gains)/Losses Recognized in Earnings and Other Comprehensive Income - Reclassified from AOCI	(10)	0	(19)	(2)
Income Statement Location [Axis]: us-gaap:CostOfRevenue | Foreign exchange contracts | Cash Flow Hedging | Financing
Derivative Instruments, Gain (Loss)
(Gains)/Losses Recognized in Earnings and Other Comprehensive Income - Reclassified from AOCI	1	1	2	2
Income Statement Location [Axis]: us-gaap:CostOfRevenue | Foreign exchange contracts | Net Investment Hedging
Derivative Instruments, Gain (Loss)
(Gains)/Losses Recognized in Earnings and Other Comprehensive Income - Amounts Excluded from Effectiveness Testing	(3)	(5)	(11)	(13)
Income Statement Location [Axis]: us-gaap:InterestExpense | Interest rate contracts | Fair Value Hedging
Derivative Instruments, Gain (Loss)
(Gains)/losses recognized on derivatives	103	(6)	165	(79)
(Gains)/losses recognized in earnings attributable to risk being hedged	(94)	22	(142)	123
Income Statement Location [Axis]: us-gaap:InterestExpense | Interest rate contracts | Cash Flow Hedging
Derivative Instruments, Gain (Loss)
(Gains)/Losses Recognized in Earnings and Other Comprehensive Income - Reclassified from AOCI	2	3	7	9
Income Statement Location [Axis]: us-gaap:InterestExpense | Foreign exchange contracts | Cash Flow Hedging
Derivative Instruments, Gain (Loss)
(Gains)/Losses Recognized in Earnings and Other Comprehensive Income - Reclassified from AOCI	3	3	9	9
Income Statement Location [Axis]: us-gaap:InterestExpense | Foreign exchange contracts | Net Investment Hedging
Derivative Instruments, Gain (Loss)
(Gains)/Losses Recognized in Earnings and Other Comprehensive Income - Amounts Excluded from Effectiveness Testing	(15)	(26)	(48)	(72)
Income Statement Location [Axis]: us-gaap:SellingGeneralAndAdministrativeExpense | Foreign exchange contracts | Cash Flow Hedging
Derivative Instruments, Gain (Loss)
(Gains)/Losses Recognized in Earnings and Other Comprehensive Income - Reclassified from AOCI	(4)	1	(7)	(1)
Income Statement Location [Axis]: ibm:OtherExpenseAndIncome | Foreign exchange contracts | Cash Flow Hedging
Derivative Instruments, Gain (Loss)
(Gains)/Losses Recognized in Earnings and Other Comprehensive Income - Reclassified from AOCI	$ (44)	$ 51	$ 288	$ (763)