NONINTEREST INCOME - Components of Revenue from Contracts with Customers (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2022	Mar. 31, 2021
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	$ 300	$ 285
Total noninterest income	498	542
Bank-owned life insurance income	21	14
Operating Segments
Disaggregation of Revenue [Line Items]
Total revenue from other sources	198	257
Total noninterest income	498	542
Consumer Banking
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	181	179
Consumer Banking | Operating Segments
Disaggregation of Revenue [Line Items]
Total revenue from other sources	76	172
Total noninterest income	257	351
Commercial Banking
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	117	106
Commercial Banking | Operating Segments
Disaggregation of Revenue [Line Items]
Total revenue from other sources	96	64
Total noninterest income	213	170
Other
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	2	0
Other | Operating Segments
Disaggregation of Revenue [Line Items]
Total revenue from other sources	26	21
Total noninterest income	28	21
Service charges and fees
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	97	99
Service charges and fees | Consumer Banking
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	69	74
Service charges and fees | Commercial Banking
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	27	25
Service charges and fees | Other
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	1	0
Card fees
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	60	54
Card fees | Consumer Banking
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	50	47
Card fees | Commercial Banking
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	10	7
Card fees | Other
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0	0
Capital markets fees
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	78	72
Capital markets fees | Consumer Banking
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0	0
Capital markets fees | Commercial Banking
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	78	72
Capital markets fees | Other
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0	0
Trust and investment services fees
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	61	58
Trust and investment services fees | Consumer Banking
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	61	58
Trust and investment services fees | Commercial Banking
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0	0
Trust and investment services fees | Other
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0	0
Other banking fees
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	4	2
Other banking fees | Consumer Banking
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	1	0
Other banking fees | Commercial Banking
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	2	2
Other banking fees | Other
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	$ 1	$ 0