Derivative Financial Instruments - Effect of Hedge Activity on Income and Expense (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)
(Gains)/Losses of Total Hedge Activity	$ 117	$ (601)	$ 540	$ (1,043)
Income Statement Location [Axis]: us-gaap:CostOfRevenue | Services
Derivative Instruments, Gain (Loss)
(Gains)/Losses of Total Hedge Activity	22	4	37	5
Income Statement Location [Axis]: us-gaap:CostOfRevenue | Sales
Derivative Instruments, Gain (Loss)
(Gains)/Losses of Total Hedge Activity	(8)	5	(9)	(2)
Income Statement Location [Axis]: us-gaap:CostOfRevenue | Financing
Derivative Instruments, Gain (Loss)
(Gains)/Losses of Total Hedge Activity	(1)	0	(2)	(1)
Income Statement Location [Axis]: us-gaap:InterestExpense
Derivative Instruments, Gain (Loss)
(Gains)/Losses of Total Hedge Activity	(3)	(3)	(8)	(5)
Income Statement Location [Axis]: us-gaap:SellingGeneralAndAdministrativeExpense
Derivative Instruments, Gain (Loss)
(Gains)/Losses of Total Hedge Activity	(164)	(114)	(97)	(83)
Income Statement Location [Axis]: ibm:OtherExpenseAndIncome
Derivative Instruments, Gain (Loss)
(Gains)/Losses of Total Hedge Activity	$ 117	$ (601)	$ 540	$ (1,043)