Significant Accounting Policies - Transfers of Financial Assets (Details) - USD ($) $ in Billions	12 Months Ended
Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Significant Accounting Policies
Gross proceeds from transfers of financial assets	$ 3.1	$ 2.1	$ 2.2
Accounts receivable sold and derecognized that remain uncollected from customers	$ 0.5	$ 0.5	$ 0.9

For transfers of receivables accounted for as sales, the amount of the receivables sold and derecognized that remains uncollected from customers as of the balance sheet date.

No definition available.

Name:	ibm_TransferOfFinancialAssetsAccountedForAsSalesAmountRemainingUncollected
Namespace Prefix:	ibm_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant