NONINTEREST INCOME - Components of Revenue from Contracts with Customers (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	$ 310	$ 322	$ 942	$ 961
Total revenue from other sources	182	190	541	543
Total noninterest income	492	512	1,483	1,504
Bank-owned life insurance income	24	22	70	64
Other
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	1	1	1	4
Total revenue from other sources	33	28	92	46
Total noninterest income	34	29	93	50
Consumer Banking | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	198	194	586	574
Total revenue from other sources	80	76	216	233
Total noninterest income	278	270	802	807
Commercial Banking | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	111	127	355	383
Total revenue from other sources	69	86	233	264
Total noninterest income	180	213	588	647
Non-Core | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0	0	0	0
Total revenue from other sources	0	0	0	0
Total noninterest income	0	0	0	0
Service charges and fees
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	105	108	305	314
Service charges and fees | Other
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	1	1	1	3
Service charges and fees | Consumer Banking | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	73	74	206	217
Service charges and fees | Commercial Banking | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	31	33	98	94
Service charges and fees | Non-Core | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0	0	0	0
Card fees
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	74	70	223	200
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	62	59	188	169
Card fees | Commercial Banking | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	12	11	35	31
Card fees | Non-Core | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0	0	0	0
Capital markets fees
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	64	76	211	244
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	64	76	211	244
Capital markets fees | Non-Core | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0	0	0	0
Trust and investment services fees
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	63	61	191	188
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	62	61	190	188
Trust and investment services fees | Commercial Banking | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	1	0	1	0
Trust and investment services fees | Non-Core | 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	4	7	12	15
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	1	0	2	0
Other banking fees | Commercial Banking | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	3	7	10	14
Other banking fees | Non-Core | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	$ 0	$ 0	$ 0	$ 0