BUSINESS SEGMENTS - Financial Information for Segments (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2022	Mar. 31, 2021	Dec. 31, 2021
Segment Reporting Information [Line Items]
Interest income	$ 254	$ 251
Interest expense	20	28
Net Interest Income	234	223
Provision for credit losses	18	6
Non-interest income	78	83
Non-interest expense	224	182
Amortization of intangibles	3	3
Income tax expense (benefit)	14	22
Net income (loss)	53	93
Total assets	42,022	38,475	$ 39,513
Total intangibles	2,493	2,313
Operating Segments | Community Banking
Segment Reporting Information [Line Items]
Interest income	253	251
Interest expense	17	25
Net Interest Income	236	226
Provision for credit losses	17	6
Non-interest income	56	63
Non-interest expense	207	165
Amortization of intangibles	3	3
Income tax expense (benefit)	14	22
Net income (loss)	51	93
Total assets	41,896	38,360
Total intangibles	2,457	2,276
Operating Segments | Wealth Management
Segment Reporting Information [Line Items]
Interest income	0	0
Interest expense	0	0
Net Interest Income	0	0
Provision for credit losses	0	0
Non-interest income	16	15
Non-interest expense	11	10
Amortization of intangibles	0	0
Income tax expense (benefit)	1	1
Net income (loss)	4	4
Total assets	38	40
Total intangibles	9	9
Operating Segments | Insurance
Segment Reporting Information [Line Items]
Interest income	0	0
Interest expense	0	0
Net Interest Income	0	0
Provision for credit losses	0	0
Non-interest income	7	6
Non-interest expense	5	5
Amortization of intangibles	0	0
Income tax expense (benefit)	0	0
Net income (loss)	2	1
Total assets	33	34
Total intangibles	27	28
Parent and Other
Segment Reporting Information [Line Items]
Interest income	1	0
Interest expense	3	3
Net Interest Income	(2)	(3)
Provision for credit losses	1	0
Non-interest income	(1)	(1)
Non-interest expense	1	2
Amortization of intangibles	0	0
Income tax expense (benefit)	(1)	(1)
Net income (loss)	(4)	(5)
Total assets	55	41
Total intangibles	$ 0	$ 0