NONINTEREST INCOME - Components of Revenue from Contracts with Customers (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	$ 298	$ 283	$ 578	$ 548
Consumer Banking
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	207	194	401	384
Commercial Banking
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	91	89	177	164
Service charges and fees
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	125	127	248	251
Service charges and fees | Consumer Banking
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	99	100	196	198
Service charges and fees | Commercial Banking
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	26	27	52	53
Card fees
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	64	60	123	121
Card fees | Consumer Banking
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	55	51	105	103
Card fees | Commercial Banking
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	9	9	18	18
Capital markets fees
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	53	51	102	88
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	53	51	102	88
Trust and investment services fees
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	53	43	100	83
Trust and investment services fees | Consumer Banking
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	53	43	100	83
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	3	2	5	5
Other banking fees | Consumer Banking
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0	0	0	0
Other banking fees | Commercial Banking
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	$ 3	$ 2	$ 5	$ 5