Basis of Presentation (Details) $ in Millions	3 Months Ended
	Mar. 31, 2022 USD ($)	Mar. 31, 2021 USD ($)		Dec. 31, 2021 USD ($)	Nov. 03, 2021
Provision for/(benefit from) income taxes	$ (39.0)	$ (160.0)	[1]
Effective tax rate (as a percent)	(6.30%)	(65.50%)
Common Stocks, Including Additional Paid in Capital	$ 57,603.0			$ 57,319.0
Retained earnings	153,401.0			$ 154,209.0
Other (income) and expense
Noncontrolling interest amounts, net of tax	4.9	$ 4.9
Kyndryl Holdings, Inc
Total of Kyndryl stock distributed to IBM stockholders of record as of 10/25/2021 (as a percentage)					80.10%
Ownership interest by stockholders (in percent)					19.90%
Revision of Prior Period, Reclassification, Adjustment
Common Stocks, Including Additional Paid in Capital	63.0
Retained earnings	$ (63.0)
Kyndryl Holdings, Inc
Total of Kyndryl stock distributed to IBM stockholders of record as of 10/25/2021 (as a percentage)					80.10%
Share conversion ratio					0.2

[1] Reclassified to reflect discontinued operations presentation.