NONINTEREST INCOME - Components of Revenue from Contracts with Customers (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2023	Jun. 30, 2022	Jun. 30, 2023	Jun. 30, 2022
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	$ 323	$ 339	$ 632	$ 639
Total revenue from other sources	183	155	359	353
Total noninterest income	506	494	991	992
Bank-owned life insurance income	23	21	46	42
Other
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0	1	0	3
Total revenue from other sources	31	(8)	59	18
Total noninterest income	31	(7)	59	21
Consumer Banking | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	198	199	388	380
Total revenue from other sources	70	81	136	157
Total noninterest income	268	280	524	537
Commercial Banking | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	125	139	244	256
Total revenue from other sources	82	82	164	178
Total noninterest income	207	221	408	434
Service charges and fees
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	101	108	200	205
Service charges and fees | Other
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0	1	0	2
Service charges and fees | Consumer Banking | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	66	73	133	142
Service charges and fees | Commercial Banking | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	35	34	67	61
Card fees
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	78	70	149	130
Card fees | Other
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0	0	0	0
Card fees | Consumer Banking | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	67	60	126	110
Card fees | Commercial Banking | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	11	10	23	20
Capital markets fees
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	76	90	147	168
Capital markets fees | Other
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0	0	0	0
Capital markets fees | Consumer Banking | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0	0	0	0
Capital markets fees | Commercial Banking | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	76	90	147	168
Trust and investment services fees
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	65	66	128	127
Trust and investment services fees | Other
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0	0	0	0
Trust and investment services fees | Consumer Banking | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	65	66	128	127
Trust and investment services fees | Commercial Banking | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0	0	0	0
Other banking fees
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	3	5	8	9
Other banking fees | Other
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0	0	0	1
Other banking fees | Consumer Banking | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0	0	1	1
Other banking fees | Commercial Banking | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	$ 3	$ 5	$ 7	$ 7