INVESTMENTS - Debt Securities Held-to-Maturity (Details) - USD ($) $ in Millions	1 Months Ended	3 Months Ended
	Jan. 31, 2023	Mar. 31, 2023		Mar. 31, 2022		Dec. 31, 2022	Dec. 31, 2021
Held-to-maturity debt securities
Amortized cost, net		$ 264,342				$ 268,863
Gross unrealized gains		76				101
Gross unrealized losses		21,567				25,316
Fair value		242,851				243,648
Allowance for credit losses on HTM debt securities		104		$ 85		120	$ 87
Transfer of investment securities from HTM to AFS	$ 3,400	3,324	[1],[2],[3]	$ 0	[1],[2],[3]
Transfer of securities from HTM to AFS, unrealized gain	$ 100
Fair value		242,851				243,648
Mortgage-backed securities - U.S. government-sponsored agency guaranteed
Held-to-maturity debt securities
Amortized cost, net		85,580				90,063
Gross unrealized gains		13				58
Gross unrealized losses		8,611				10,033
Fair value		76,982				80,088
Fair value		76,982				80,088
Mortgage-backed securities - Non-U.S. residential
Held-to-maturity debt securities
Amortized cost, net		409				445
Gross unrealized gains		0				0
Gross unrealized losses		0				0
Fair value		409				445
Fair value		409				445
Commercial
Held-to-maturity debt securities
Amortized cost, net		1,119				1,114
Gross unrealized gains		0				5
Gross unrealized losses		158				1
Fair value		961				1,118
Fair value		961				1,118
Mortgage-backed securities
Held-to-maturity debt securities
Amortized cost, net		87,108				91,622
Gross unrealized gains		13				63
Gross unrealized losses		8,769				10,034
Fair value		78,352				81,651
Fair value		78,352				81,651
U.S. treasury securities
Held-to-maturity debt securities
Amortized cost, net		134,952				134,961
Gross unrealized gains		0				0
Gross unrealized losses		11,505				13,722
Fair value		123,447				121,239
Fair value		123,447				121,239
State and municipal
Held-to-maturity debt securities
Amortized cost, net		9,212				9,237
Gross unrealized gains		63				34
Gross unrealized losses		556				764
Fair value		8,719				8,507
Fair value		8,719				8,507
Foreign government
Held-to-maturity debt securities
Amortized cost, net		2,244				2,075
Gross unrealized gains		0				0
Gross unrealized losses		103				93
Fair value		2,141				1,982
Fair value		2,141				1,982
Asset-backed securities
Held-to-maturity debt securities
Amortized cost, net		30,826				30,968
Gross unrealized gains		0				4
Gross unrealized losses		634				703
Fair value		30,192				30,269
Fair value		$ 30,192				$ 30,269

[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. See Note 1.

[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 24 for more information and balances as of March 31, 2023.

[3] See Note 2 for further information on significant disposals.