GOODWILL AND INTANGIBLE ASSETS - Changes in Goodwill by Segment (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Mar. 31, 2022	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Goodwill
Balance of goodwill at beginning of period	$ 21,299	$ 19,691	$ 21,299	$ 22,162
Foreign exchange translation		407	(200)	(383)
Divestitures			(873)	(480)
Impairment of goodwill	(535)	0	(535)	0
Balance of goodwill at end of period		20,098	19,691	21,299
Goodwill impairment, after-tax	489
All Other
Goodwill
Balance of goodwill at beginning of period	2,367	964	2,367	2,659
Foreign exchange translation		144	5	179
Divestitures			(873)	(471)
Impairment of goodwill			(535)
Balance of goodwill at end of period		1,108	964	2,367
Services | Operating Segments
Goodwill
Balance of goodwill at beginning of period	2,105	2,167	2,105	2,166
Foreign exchange translation		47	62	(61)
Divestitures			0	0
Impairment of goodwill			0
Balance of goodwill at end of period		2,214	2,167	2,105
Markets
Goodwill
Goodwill transferred to (from)		537
Markets | Operating Segments
Goodwill
Balance of goodwill at beginning of period	6,078	5,785	6,078	6,238
Foreign exchange translation		85	(293)	(160)
Divestitures			0	0
Impairment of goodwill			0
Balance of goodwill at end of period		5,870	5,785	6,078
Banking
Goodwill
Goodwill transferred to (from)		(537)
Banking | Operating Segments
Goodwill
Balance of goodwill at beginning of period	1,032	1,034	1,032	1,077
Foreign exchange translation		5	2	(45)
Divestitures			0	0
Impairment of goodwill			0
Balance of goodwill at end of period		1,039	1,034	1,032
USPB | Operating Segments
Goodwill
Balance of goodwill at beginning of period	5,223	5,273	5,223	5,387
Foreign exchange translation		125	50	(164)
Divestitures			0	0
Impairment of goodwill			0
Balance of goodwill at end of period		5,398	5,273	5,223
Wealth | Operating Segments
Goodwill
Balance of goodwill at beginning of period	$ 4,494	4,468	4,494	4,635
Foreign exchange translation		1	(26)	(132)
Divestitures			0	(9)
Impairment of goodwill			0
Balance of goodwill at end of period		$ 4,469	$ 4,468	$ 4,494