Derivative Financial Instruments - Effect of Hedge Activity on Income and Expense (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)
(Gains)/Losses of Total Hedge Activity	$ 21	$ 162	$ 560	$ (881)
Income Statement Location [Axis]: us-gaap:CostOfRevenue | Services
Derivative Instruments, Gain (Loss)
(Gains)/Losses of Total Hedge Activity	20	7	57	12
Income Statement Location [Axis]: us-gaap:CostOfRevenue | Sales
Derivative Instruments, Gain (Loss)
(Gains)/Losses of Total Hedge Activity	(10)	0	(19)	(2)
Income Statement Location [Axis]: us-gaap:CostOfRevenue | Financing
Derivative Instruments, Gain (Loss)
(Gains)/Losses of Total Hedge Activity	0	(1)	(2)	(2)
Income Statement Location [Axis]: us-gaap:InterestExpense
Derivative Instruments, Gain (Loss)
(Gains)/Losses of Total Hedge Activity	(1)	(4)	(9)	(9)
Income Statement Location [Axis]: us-gaap:SellingGeneralAndAdministrativeExpense
Derivative Instruments, Gain (Loss)
(Gains)/Losses of Total Hedge Activity	37	(74)	(60)	(157)
Income Statement Location [Axis]: ibm:OtherExpenseAndIncome
Derivative Instruments, Gain (Loss)
(Gains)/Losses of Total Hedge Activity	$ 21	$ 162	$ 560	$ (881)