Financial Assets & Liabilities - Fair Value Measurements (Details) - USD ($) $ in Millions	Jun. 30, 2026	Dec. 31, 2025
Financial assets and financial liabilities measured at fair value on a recurring basis:
Cash equivalents	$ 1,915	$ 7,485
Debt securities - current	960	830
Total assets	3,805	8,916
Total liabilities	595	513
Balance Sheet Location [Axis]: us-gaap:InvestmentsAndOtherNoncurrentAssets
Financial assets and financial liabilities measured at fair value on a recurring basis:
Derivative assets	161	361
Balance Sheet Location [Axis]: us-gaap:OtherLiabilitiesNoncurrent
Financial assets and financial liabilities measured at fair value on a recurring basis:
Derivative liabilities	402	259
Balance Sheet Location [Axis]: us-gaap:PrepaidExpenseAndOtherAssetsCurrent
Financial assets and financial liabilities measured at fair value on a recurring basis:
Derivative assets	662	232
Balance Sheet Location [Axis]: ibm:AccruedLiabilitiesAndOtherLiabilitiesCurrent
Financial assets and financial liabilities measured at fair value on a recurring basis:
Derivative liabilities	192	254
Level 1
Financial assets and financial liabilities measured at fair value on a recurring basis:
Equity investments	96	0
Level 1 | Money market funds
Financial assets and financial liabilities measured at fair value on a recurring basis:
Cash equivalents	48	413
Level 2
Financial assets and financial liabilities measured at fair value on a recurring basis:
Debt securities - current	960	830
Level 2 | Interest rate contracts
Financial assets and financial liabilities measured at fair value on a recurring basis:
Derivatives designated as hedging - Assets	1	2
Derivatives designated as hedging - Liabilities	209	171
Level 2 | Foreign exchange contracts
Financial assets and financial liabilities measured at fair value on a recurring basis:
Derivatives designated as hedging - Assets	760	545
Derivatives designated as hedging - Liabilities	347	325
Derivatives not designated as hedging - Assets	29	12
Derivatives not designated as hedging - Liabilities	36	14
Level 2 | Equity contracts
Financial assets and financial liabilities measured at fair value on a recurring basis:
Derivatives not designated as hedging - Assets	33	34
Derivatives not designated as hedging - Liabilities	2	3
Level 2 | Time deposits, certificates of deposit and other
Financial assets and financial liabilities measured at fair value on a recurring basis:
Cash equivalents	1,867	7,072
Level 2 And 3
Financial assets and financial liabilities measured at fair value on a recurring basis:
Debt securities - noncurrent	$ 12	$ 9