NONINTEREST INCOME - Components of Revenue from Contracts with Customers (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	$ 1,172	$ 1,119
Consumer Banking
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	818	786
Commercial Banking
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	354	333
Service charges and fees
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	503	513
Service charges and fees | Consumer Banking
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	400	408
Service charges and fees | Commercial Banking
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	103	105
Card fees
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	254	244
Card fees | Consumer Banking
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	215	207
Card fees | Commercial Banking
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	39	37
Capital markets fees
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	202	181
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	202	181
Trust and investment services fees
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	202	171
Trust and investment services fees | Consumer Banking
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	202	171
Trust and investment services fees | Commercial Banking
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	11	10
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	$ 10	$ 10