BASIS OF PRESENTATION, UPDATED ACCOUNTING POLICIES AND ACCOUNTING CHANGES (Details) - USD ($) $ in Millions		1 Months Ended	6 Months Ended
		Jan. 31, 2023	Jun. 30, 2024		Jun. 30, 2023		Mar. 31, 2024	Dec. 31, 2023	Mar. 31, 2023	Dec. 31, 2022
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Allowance for credit losses			$ (18,216)		$ (17,496)		$ (18,296)	$ (18,145)	$ (17,169)	$ (16,974)
Other assets, at fair value			99,569					95,963
Stockholders’ equity			209,144		209,422			206,251
Other liabilities			(69,304)					(75,835)
Transfer of investment securities from HTM to AFS, amortized cost		$ 3,300	0	[1],[2],[3]	3,324	[1],[2],[3]
Cumulative Effect, Period of Adoption, Adjustment
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Allowance for credit losses										352
Retained earnings
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Stockholders’ equity			202,913		199,976		200,956	198,905	198,353	194,734
Retained earnings | Cumulative Effect, Period of Adoption, Adjustment
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Stockholders’ equity	[4]									290
Accumulated other comprehensive income (loss)
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Stockholders’ equity			$ (46,677)		$ (45,865)		$ (45,729)	$ (44,800)	$ (45,441)	(47,062)
Accumulated other comprehensive income (loss) | Cumulative Effect, Period of Adoption, Adjustment
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Stockholders’ equity	[5]									$ 27

[1] 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 26 for more information and balances as of June 30, 2024.

[2] See Note 2.

[3] n 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.

[4] See “Accounting Changes” in Note 1 to the Consolidated Financial Statements in Citi’s 2023 Form 10-K.

[5] See Note 1 to the Consolidated Financial Statements in Citi’s 2023 Form 10-K.