Basis of Presentation (Details) $ in Millions			3 Months Ended			6 Months Ended
	May 23, 2022 shares	May 19, 2022 shares	Jun. 30, 2022 USD ($)	Jun. 30, 2021 USD ($)		Jun. 30, 2022 USD ($)	Jun. 30, 2021 USD ($)		Mar. 31, 2022 USD ($)	Dec. 31, 2021 USD ($)	Nov. 03, 2021
Provision for/(benefit from) income taxes			$ 257.0	$ 101.0	[1]	$ 218.0	$ (58.0)	[1]
Effective tax rate (as a percent)			14.90%	11.10%		9.30%	(5.00%)
Numbers shares transferred | shares		22,300,000
Common Stocks, Including Additional Paid in Capital			$ 57,802.0			$ 57,802.0				$ 57,319.0
Retained earnings			153,298.0			153,298.0				$ 154,209.0
Other (income) and expenses
Noncontrolling interest amounts, net of tax			$ 5.5	$ 4.2		$ 10.5	$ 9.1
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%
Numbers shares transferred | shares	22,301,536
Amount of retained interest transferred	9.95%
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.