DISCONTINUED OPERATIONS, SIGNIFICANT DISPOSALS AND OTHER BUSINESS EXITS - Narrative (Details) - Citibank Korea Inc. - Employee Severance Costs - USD ($) $ in Millions	3 Months Ended
Mar. 31, 2022	Oct. 25, 2021
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Pretax charges recorded from other business exits	$ 31.0
Total estimated cash charges for the wind-down		$ 1,100.0

Amount of expenses associated with exit or disposal activities pursuant to an authorized plan. Excludes expenses related to a discontinued operation or an asset retirement obligation.

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