GOODWILL AND INTANGIBLE ASSETS - Changes in Goodwill (Details) - USD ($) $ in Millions	3 Months Ended			9 Months Ended
	Sep. 30, 2025	Jun. 30, 2025	Mar. 31, 2025	Sep. 30, 2025	Sep. 30, 2024
Goodwill
Balance at December 31, 2024	$ 19,878	$ 19,422	$ 19,300	$ 19,300
Foreign currency translation	(26)	456	122
Impairment of goodwill	(726)			(726)	$ 0
Balance at September 30, 2025	19,126	19,878	19,422	19,126
Mexico Consumer/SBMM businesses
Goodwill
Impairment of goodwill	(726)
Impairment loss, after tax	714
All Other
Goodwill
Balance at December 31, 2024	1,002	919	902	902
Foreign currency translation	20	83	17
Impairment of goodwill	(726)
Balance at September 30, 2025	296	1,002	919	296
Services | Operating Segments
Goodwill
Balance at December 31, 2024	2,172	2,063	2,052	2,052
Foreign currency translation	(19)	109	11
Impairment of goodwill	0
Balance at September 30, 2025	2,153	2,172	2,063	2,153
Markets | Operating Segments
Goodwill
Balance at December 31, 2024	5,920	5,749	5,674	5,674
Foreign currency translation	(49)	171	75
Impairment of goodwill	0
Balance at September 30, 2025	5,871	5,920	5,749	5,871
Banking | Operating Segments
Goodwill
Balance at December 31, 2024	1,025	1,005	1,002	1,002
Foreign currency translation	1	20	3
Impairment of goodwill	0
Balance at September 30, 2025	1,026	1,025	1,005	1,026
USPB | Operating Segments
Goodwill
Balance at December 31, 2024	5,306	5,235	5,219	5,219
Foreign currency translation	21	71	16
Impairment of goodwill	0
Balance at September 30, 2025	5,327	5,306	5,235	5,327
Wealth | Operating Segments
Goodwill
Balance at December 31, 2024	4,453	4,451	4,451	4,451
Foreign currency translation	0	2	0
Impairment of goodwill	0
Balance at September 30, 2025	$ 4,453	$ 4,453	$ 4,451	$ 4,453