DISCONTINUED OPERATIONS, SIGNIFICANT DISPOSALS AND OTHER BUSINESS EXITS - Summarized Reserve Charges (Details) - Citibank Korea Inc. - Severance costs - USD ($) $ in Millions	2 Months Ended	3 Months Ended
	Dec. 31, 2021	Jun. 30, 2022	Mar. 31, 2022
Employee termination costs
Beginning of period	$ 1,052	$ 714	$ 1,054
Additional charges		(3)	31
Utilization	(1)	(670)	(347)
Foreign exchange	3	(41)	(24)
End of period	$ 1,054	$ 0	$ 714