NONINTEREST INCOME - Components of Revenue from Contracts with Customers (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2022	Jun. 30, 2021	Jun. 30, 2022	Jun. 30, 2021
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	$ 339	$ 310	$ 639	$ 595
Total noninterest income	494	485	992	1,027
Bank-owned life insurance income	21	16	42	30
Operating Segments
Disaggregation of Revenue [Line Items]
Total revenue from other sources	155	175	353	432
Total noninterest income	494	485	992	1,027
Other
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	1	0	3	0
Total revenue from other sources	(8)	24	18	45
Total noninterest income	(7)	24	21	45
Consumer Banking
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	199	190	380	369
Consumer Banking | Operating Segments
Disaggregation of Revenue [Line Items]
Total revenue from other sources	81	93	157	265
Total noninterest income	280	283	537	634
Commercial Banking
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	139	120	256	226
Commercial Banking | Operating Segments
Disaggregation of Revenue [Line Items]
Total revenue from other sources	82	58	178	122
Total noninterest income	221	178	434	348
Service charges and fees
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	108	100	205	199
Service charges and fees | Other
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	1	0	2	0
Service charges and fees | Consumer Banking
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	73	74	142	148
Service charges and fees | Commercial Banking
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	34	26	61	51
Card fees
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	70	64	130	118
Card fees | Other
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0	0	0	0
Card fees | Consumer Banking
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	60	56	110	103
Card fees | Commercial Banking
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	10	8	20	15
Capital markets fees
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	90	84	168	156
Capital markets fees | Other
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0	0	0	0
Capital markets fees | Consumer Banking
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0	0	0	0
Capital markets fees | Commercial Banking
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	90	84	168	156
Trust and investment services fees
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	66	60	127	118
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
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	66	60	127	118
Trust and investment services fees | Commercial Banking
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	5	2	9	4
Other banking fees | Other
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0	0	1	0
Other banking fees | Consumer Banking
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0	0	1	0
Other banking fees | Commercial Banking
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	$ 5	$ 2	$ 7	$ 4