DEPOSITS (Details) - USD ($) $ in Millions		3 Months Ended
		Mar. 31, 2025	Mar. 31, 2024	Dec. 31, 2024
Deposit Liability [Line Items]
Non-interest-bearing deposits in U.S. offices		$ 122,472		$ 123,338
Interest-bearing deposits in U.S. offices (including $1,534 and $1,262 as of March 31, 2025 and December 31, 2024, respectively, at fair value)		562,628		551,547
Total deposits in U.S. offices		685,100		674,885
Non-interest-bearing deposits in offices outside the U.S. (including $442 million and $383 million as of March 31, 2025 and December 31, 2024, respectively, at fair value)		82,215		84,349
Interest-bearing deposits in offices outside the U.S. (including $2,250 and $1,963 as of March 31, 2025 and December 31, 2024, respectively, at fair value)		549,095		525,224
Total deposits in offices outside the U.S.		631,310		609,573
Total deposits		1,316,410		1,284,458
Other operating	[1]	1,349	$ 1,820
Silicon Valley Bank And Signature Bank
Deposit Liability [Line Items]
Other operating		20	$ 251
Fair value
Deposit Liability [Line Items]
Interest-bearing deposits in U.S. offices (including $1,534 and $1,262 as of March 31, 2025 and December 31, 2024, respectively, at fair value)		1,534		1,262
Non-interest-bearing deposits in offices outside the U.S. (including $442 million and $383 million as of March 31, 2025 and December 31, 2024, respectively, at fair value)		442		383
Interest-bearing deposits in offices outside the U.S. (including $2,250 and $1,963 as of March 31, 2025 and December 31, 2024, respectively, at fair value)		2,250		1,963
Total deposits		$ 1,312,200		$ 1,280,900

[1]     Effective January 1, 2025, certain transaction processing fees paid by Citi, primarily to credit card networks, which were previously presented within Other operating expenses, are presented as contra-revenue within Commissions and fees reported in Non-interest revenue. Prior periods were conformed to reflect this change in presentation.