BUSINESS SEGMENTS - Financial Information for Segments (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2022	Jun. 30, 2021	Jun. 30, 2022	Jun. 30, 2021	Dec. 31, 2021
Segment Reporting Information [Line Items]
Interest income	$ 280	$ 253	$ 534	$ 504
Interest expense	26	25	46	53
Net Interest Income	254	228	488	451
Provision for credit losses	6	(1)	24	5
Non-interest income	82	80	160	163
Non-interest expense	189	179	413	361
Amortization of intangibles	4	3	7	6
Income tax expense (benefit)	28	25	42	47
Net income (loss)	109	102	162	195
Total Assets	41,681	38,406	41,681	38,406	$ 39,513
Total intangibles	2,489	2,310	2,489	2,310
Operating Segments | Community Banking
Segment Reporting Information [Line Items]
Interest income	279	253	532	504
Interest expense	24	22	41	47
Net Interest Income	255	231	491	457
Provision for credit losses	6	(2)	23	4
Non-interest income	61	60	117	123
Non-interest expense	173	162	380	327
Amortization of intangibles	3	2	6	5
Income tax expense (benefit)	28	26	42	48
Net income (loss)	106	103	157	196
Total Assets	41,545	38,288	41,545	38,288
Total intangibles	2,453	2,273	2,453	2,273
Operating Segments | Wealth Management
Segment Reporting Information [Line Items]
Interest income	0	0	0	0
Interest expense	0	0	0	0
Net Interest Income	0	0	0	0
Provision for credit losses	0	0	0	0
Non-interest income	16	15	32	30
Non-interest expense	10	10	21	20
Amortization of intangibles	0	0	0	0
Income tax expense (benefit)	1	1	2	2
Net income (loss)	5	4	9	8
Total Assets	37	42	37	42
Total intangibles	9	9	9	9
Operating Segments | Insurance
Segment Reporting Information [Line Items]
Interest income	0	0	0	0
Interest expense	0	0	0	0
Net Interest Income	0	0	0	0
Provision for credit losses	0	0	0	0
Non-interest income	6	7	13	13
Non-interest expense	4	5	9	10
Amortization of intangibles	1	1	1	1
Income tax expense (benefit)	1	1	1	1
Net income (loss)	0	0	2	1
Total Assets	35	35	35	35
Total intangibles	27	28	27	28
Parent and Other
Segment Reporting Information [Line Items]
Interest income	1	0	2	0
Interest expense	2	3	5	6
Net Interest Income	(1)	(3)	(3)	(6)
Provision for credit losses	0	1	1	1
Non-interest income	(1)	(2)	(2)	(3)
Non-interest expense	2	2	3	4
Amortization of intangibles	0	0	0	0
Income tax expense (benefit)	(2)	(3)	(3)	(4)
Net income (loss)	(2)	(5)	(6)	(10)
Total Assets	64	41	64	41
Total intangibles	$ 0	$ 0	$ 0	$ 0