Financial Assets & Liabilities - Fair Value Measurements (Details) - USD ($) $ in Millions	Sep. 30, 2026	Dec. 31, 2025
Financial assets and financial liabilities measured at fair value on a recurring basis:
Cash equivalents	$ 4,129	$ 7,485
Debt securities - current	1,825	830
Total assets	6,670	8,916
Total liabilities	728	513
Balance Sheet Location [Axis]: us-gaap:InvestmentsAndOtherNoncurrentAssets
Financial assets and financial liabilities measured at fair value on a recurring basis:
Derivative assets	128	361
Balance Sheet Location [Axis]: us-gaap:OtherLiabilitiesNoncurrent
Financial assets and financial liabilities measured at fair value on a recurring basis:
Derivative liabilities	531	259
Balance Sheet Location [Axis]: us-gaap:PrepaidExpenseAndOtherAssetsCurrent
Financial assets and financial liabilities measured at fair value on a recurring basis:
Derivative assets	521	232
Balance Sheet Location [Axis]: ibm:AccruedLiabilitiesAndOtherLiabilitiesCurrent
Financial assets and financial liabilities measured at fair value on a recurring basis:
Derivative liabilities	198	254
Level 2
Financial assets and financial liabilities measured at fair value on a recurring basis:
Debt securities - current	1,825	830
Level 2 | Interest rate contracts
Financial assets and financial liabilities measured at fair value on a recurring basis:
Derivatives designated as hedging - Assets	0	2
Derivatives designated as hedging - Liabilities	325	171
Level 2 | Foreign exchange contracts
Financial assets and financial liabilities measured at fair value on a recurring basis:
Derivatives designated as hedging - Assets	616	545
Derivatives designated as hedging - Liabilities	363	325
Derivatives not designated as hedging - Assets	21	12
Derivatives not designated as hedging - Liabilities	13	14
Level 2 | Equity contracts
Financial assets and financial liabilities measured at fair value on a recurring basis:
Derivatives not designated as hedging - Assets	11	34
Derivatives not designated as hedging - Liabilities	27	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	2,408	7,072
Level 1
Financial assets and financial liabilities measured at fair value on a recurring basis:
Equity investments	56	0
Level 1 | Money market funds
Financial assets and financial liabilities measured at fair value on a recurring basis:
Cash equivalents	1,721	413
Level 2 And 3
Financial assets and financial liabilities measured at fair value on a recurring basis:
Debt securities - noncurrent	$ 12	$ 9