GOODWILL AND INTANGIBLE ASSETS - Changes in Goodwill (Details) - USD ($) $ in Millions	3 Months Ended			12 Months Ended
	Sep. 30, 2024	Jun. 30, 2024	Mar. 31, 2024	Dec. 31, 2023
Goodwill
Balance at December 31, 2023	$ 19,704	$ 20,042	$ 20,098
Foreign currency translation	3	(338)	(56)
Divestures	(16)
Balance at March 31, 2024	19,691	19,704	20,042	$ 20,098
All Other
Goodwill
Balance at December 31, 2023	1,028	1,136	1,108
Foreign currency translation	(73)	(108)	28
Divestures	0
Balance at March 31, 2024	955	1,028	1,136	1,108
Services | Operating Segments
Goodwill
Balance at December 31, 2023	2,130	2,187	2,214
Foreign currency translation	13	(57)	(27)
Divestures	0
Balance at March 31, 2024	2,143	2,130	2,187	2,214
Markets
Goodwill
Reallocation of goodwill due to reorganization of reportable operating segments				537
Markets | Operating Segments
Goodwill
Balance at December 31, 2023	5,726	5,788	5,870
Foreign currency translation	136	(62)	(82)
Divestures	0
Balance at March 31, 2024	5,862	5,726	5,788	5,870
Banking
Goodwill
Reallocation of goodwill due to reorganization of reportable operating segments				(537)
Banking | Operating Segments
Goodwill
Balance at December 31, 2023	1,023	1,041	1,039
Foreign currency translation	(10)	(18)	2
Divestures	0
Balance at March 31, 2024	1,013	1,023	1,041	1,039
USPB | Operating Segments
Goodwill
Balance at December 31, 2023	5,329	5,421	5,398
Foreign currency translation	(63)	(92)	23
Divestures	0
Balance at March 31, 2024	5,266	5,329	5,421	5,398
Wealth | Operating Segments
Goodwill
Balance at December 31, 2023	4,468	4,469	4,469
Foreign currency translation	0	(1)	0
Divestures	(16)
Balance at March 31, 2024	$ 4,452	$ 4,468	$ 4,469	$ 4,469