Derivative Financial Instruments - Gains and Losses (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2026	Jun. 30, 2025	Jun. 30, 2026	Jun. 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	$ (84)	$ (295)	$ 122	$ (451)
(Gains)/losses recognized in earnings attributable to risk being hedged	(31)	33	(59)	119
(Gains)/Losses Recognized in Earnings and Other Comprehensive Income - Recognized in OCI	287	(1,668)	576	(2,535)
(Gains)/Losses Recognized in Earnings and Other Comprehensive Income - Reclassified from AOCI	59	(449)	370	(798)
(Gains)/Losses Recognized in Earnings and Other Comprehensive Income - Amounts Excluded from Effectiveness Testing	17	2	27	3
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	37	(165)	139	(285)
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	68	(25)	(61)	17
(Gains)/Losses Recognized in Earnings and Other Comprehensive Income - Recognized in OCI - Amount excluded from the assessment of effectiveness	51	(57)	4	(158)
(Gains)/Losses Recognized in Earnings and Other Comprehensive Income - Amounts Excluded from Effectiveness Testing	37	30	68	56
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	(31)	0	(17)	11
(Gains)/Losses Recognized in Earnings and Other Comprehensive Income - Recognized in OCI - Net investment hedges	199	(1,585)	649	(2,406)
Equity contracts | Not Designated as Hedging Instrument, Economic Hedge
Derivative Instruments, Gain (Loss)
(Gains)/losses recognized on derivatives	(160)	(115)	(94)	(81)
Income Statement Location [Axis]: us-gaap:CostOfRevenue | Interest rate contracts | Fair Value Hedging
Derivative Instruments, Gain (Loss)
(Gains)/losses recognized on derivatives	7	(2)	14	(13)
(Gains)/losses recognized in earnings attributable to risk being hedged	(5)	5	(11)	18
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	1	0	1	1
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	22	4	37	5
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	(8)	5	(9)	(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	1	1
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)	(4)	(8)	(8)
Income Statement Location [Axis]: us-gaap:InterestExpense | Interest rate contracts | Fair Value Hedging
Derivative Instruments, Gain (Loss)
(Gains)/losses recognized on derivatives	32	(13)	63	(72)
(Gains)/losses recognized in earnings attributable to risk being hedged	(25)	28	(48)	101
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	5	6
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	6	6
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	(16)	(24)	(34)	(45)
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)	2	(3)	(2)
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	$ 43	$ (466)	$ 332	$ (814)