Amount of current income tax expense (benefit) and deferred income tax expense (benefit) pertaining to continuing operations.

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Name:	us-gaap_IncomeTaxExpenseBenefit
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

Basis of Presentation (Details) $ in Millions		3 Months Ended		9 Months Ended
Basis of Presentation (Details) $ in Millions	Nov. 03, 2021	Sep. 30, 2021 USD ($)	Sep. 30, 2020 USD ($)	Sep. 30, 2021 USD ($)	Sep. 30, 2020 USD ($)
Provision for/(benefit from) income taxes		$ 188.0	$ 128.0	$ 365.0	$ (888.0)
Other (income) and expense
Noncontrolling interest amounts, net of tax		$ 8.3	$ 3.4	$ 22.4	$ 14.7
Kyndryl Holdings, Inc
Ownership interest by stockholders (in percent)	19.90%
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