DISCONTINUED OPERATIONS, SIGNIFICANT DISPOSALS AND OTHER BUSINESS EXITS - Narrative (Details) $ in Millions			1 Months Ended	3 Months Ended	7 Months Ended	12 Months Ended
	Jan. 01, 2023 USD ($)	Dec. 12, 2022 USD ($)	Jan. 31, 2023 USD ($)	Jun. 30, 2023 USD ($)	Jun. 30, 2023 USD ($)	Dec. 31, 2023 USD ($) business		Dec. 31, 2022 USD ($)		Dec. 31, 2021 USD ($)	[1],[2],[3]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Transfer of investment securities from HTM to AFS	$ 3,300		$ 3,300			$ 3,324	[1],[2],[3]	$ 0	[1],[2],[3]	$ 0
Consumer
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Gain (loss) on sale of loans				$ 5	$ (7)
Russian Operations | Consumer
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Sales of loans		$ 240
Gain (loss) on sale of loans		(12)
Adjustment to record loans at lower of cost or fair value		32
Decrease in allowance for loans sold		$ 20
Employee Severance Costs | Russian Operations
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Credit card receivable amount refinanced						$ 47
Discontinued Operations, Disposed of by Sale | Legacy Franchises
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Loss on sale of business, foreign currency translation adjustments, pretax								400
Loss on sale of business, foreign currency translation adjustments, after-tax								345
Egg Banking Business | Discontinued Operations, Disposed of by Sale
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Loss on sale of business, foreign currency translation adjustments, pretax								260
Loss on sale of business, foreign currency translation adjustments, after-tax								221
Legacy Holdings | Discontinued Operations, Disposed of by Sale | Legacy Franchises
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Loss on sale of business, foreign currency translation adjustments, pretax								140
Loss on sale of business, foreign currency translation adjustments, after-tax								124
Consumer Banking Businesses | Discontinued Operations, Held-for-sale or Disposed of by Sale | Legacy Franchises
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Number of businesses sold | business						9
Consumer Banking Businesses | Discontinued Operations, Disposed of by Sale | Legacy Franchises
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Number of businesses sold | business						9
Number of significant businesses sold | business						5
Citibank Korea Inc. | Employee Severance Costs
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Restructuring costs incurred to date								$ 1,100

[1] In January 2023, Citi adopted ASU 2022-01. Upon adoption, Citi transferred $3.3 billion of mortgage-backed securities from HTM classification to AFS classification as allowed under the ASU. At the time of transfer, the securities were in an unrealized gain position of $0.1 billion, which was recorded in AOCI upon transfer.

[2] Operating and finance lease right-of-use assets and lease liabilities represent non-cash investing and financing activities, respectively, and are not included in the non-cash investing activities presented here. See Note 29 for more information and balances as of December 31, 2023 and 2022.

[3] See Note 2.