INVESTMENTS - Debt Securities Held-to-Maturity (Details) - USD ($) $ in Millions		1 Months Ended	12 Months Ended
	Jan. 01, 2023	Jan. 31, 2023	Dec. 31, 2024		Dec. 31, 2023		Dec. 31, 2022	[1],[2],[3]
Debt Securities Held-to-maturity
Total amortized cost			$ 242,382		$ 254,247
Gross unrecognized gains			133		91
Gross unrecognized losses			18,105		19,337
Fair value			224,410		235,001
Transfer of investment securities from HTM to AFS	$ 3,300	$ 3,300	0	[1],[2],[3]	3,324	[1],[2],[3]	$ 0
Transfer of securities from HTM to AFS, unrealized gain		$ 100
U.S. government-sponsored agency guaranteed
Debt Securities Held-to-maturity
Total amortized cost			72,542		79,689
Gross unrecognized gains			0		7
Gross unrecognized losses			10,291		8,603
Fair value			62,251		71,093
Mortgage-backed securities - Non-U.S. residential
Debt Securities Held-to-maturity
Total amortized cost			0		198
Gross unrecognized gains			0		0
Gross unrecognized losses			0		0
Fair value			0		198
Commercial
Debt Securities Held-to-maturity
Total amortized cost			1,247		1,146
Gross unrecognized gains			12		2
Gross unrecognized losses			151		156
Fair value			1,108		992
Mortgage-backed securities
Debt Securities Held-to-maturity
Total amortized cost			73,789		81,033
Gross unrecognized gains			12		9
Gross unrecognized losses			10,442		8,759
Fair value			63,359		72,283
U.S. Treasury securities
Debt Securities Held-to-maturity
Total amortized cost			126,142		131,776
Gross unrecognized gains			0		0
Gross unrecognized losses			6,934		9,908
Fair value			119,208		121,868
State and municipal
Debt Securities Held-to-maturity
Total amortized cost			8,903		9,182
Gross unrecognized gains			27		73
Gross unrecognized losses			668		477
Fair value			8,262		8,778
Foreign government
Debt Securities Held-to-maturity
Total amortized cost			988		2,210
Gross unrecognized gains			3		0
Gross unrecognized losses			0		58
Fair value			991		2,152
Asset-backed securities
Debt Securities Held-to-maturity
Total amortized cost			32,560		30,046
Gross unrecognized gains			91		9
Gross unrecognized losses			61		135
Fair value			$ 32,590		$ 29,920

[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, 2024 and 2023.

[3] See Note 2.