ACQUISITIONS - Schedule of Acquisition and Integration Costs (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2022	Jun. 30, 2021	Jun. 30, 2022	Jun. 30, 2021
Business Acquisition [Line Items]
Provision expense (benefit) for loans and leases	$ 192	$ (169)	$ 213	$ (260)
Salaries and employee benefits	683	524	1,277	1,072
Outside services	189	137	358	276
Other operating expense	153	93	263	184
Income before income tax expense	478	$ 831	1,014	$ 1,612
Investors Acquisition | Acquisition-related Costs
Business Acquisition [Line Items]
Provision expense (benefit) for loans and leases	145		145
Salaries and employee benefits	61		61
Outside services	29		36
Mark-to-market losses on LHFS portfolio	31		31
Other operating expense	2		2
Income before income tax expense	$ 268		$ 275