DEPOSITS (Details) - USD ($) $ in Millions		3 Months Ended		9 Months Ended
		Sep. 30, 2025	Sep. 30, 2024	Sep. 30, 2025	Sep. 30, 2024	Dec. 31, 2024
Deposit Liability [Line Items]
Non-interest-bearing deposits in U.S. offices		$ 116,921		$ 116,921		$ 123,338
Interest-bearing deposits in U.S. offices (including $1,878 and $1,262 as of September 30, 2025 and December 31, 2024, respectively, at fair value)		592,728		592,728		551,547
Total deposits in U.S. offices		709,649		709,649		674,885
Non-interest-bearing deposits in offices outside the U.S. (including $519 million and $383 million as of September 30, 2025 and December 31, 2024, respectively, at fair value)		83,920		83,920		84,349
Interest-bearing deposits in offices outside the U.S. (including $1,287 and $1,963 as of September 30, 2025 and December 31, 2024, respectively, at fair value)		590,360		590,360		525,224
Total deposits in offices outside the U.S.		674,280		674,280		609,573
Total deposits		1,383,929		1,383,929		1,284,458
Other operating(1)(3)	[1],[2]	2,005	$ 1,322	4,266	$ 4,571
Fair value
Deposit Liability [Line Items]
Interest-bearing deposits in U.S. offices (including $1,878 and $1,262 as of September 30, 2025 and December 31, 2024, respectively, at fair value)		1,878		1,878		1,262
Non-interest-bearing deposits in offices outside the U.S. (including $519 million and $383 million as of September 30, 2025 and December 31, 2024, respectively, at fair value)		519		519		383
Interest-bearing deposits in offices outside the U.S. (including $1,287 and $1,963 as of September 30, 2025 and December 31, 2024, respectively, at fair value)		1,287		1,287		1,963
Total deposits		$ 1,380,200		$ 1,380,200		$ 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.

[2] Effective July 1, 2025, certain expenses incurred in ongoing support of products and services that are predominantly variable costs, which were previously presented within Other operating expenses and Transactional and tax charges, are aggregated and presented within a new expenses category, Transactional and product servicing (see “Glossary” below for definition). Moreover, certain non-income tax charges incurred, which were previously presented within Transactional and tax charges and do not align with the redefined Transactional and product servicing, are presented within Other operating. Prior periods were conformed to reflect this change in presentation.