NONINTEREST INCOME - Components of Revenue from Contracts with Customers (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	$ 280	$ 265
Consumer Banking
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	194	190
Commercial Banking
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	86	75
Service charges and fees
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	123	124
Service charges and fees | Consumer Banking
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	97	98
Service charges and fees | Commercial Banking
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	26	26
Card fees
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	59	61
Card fees | Consumer Banking
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	50	52
Card fees | Commercial Banking
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	9	9
Capital markets fees
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	49	37
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	49	37
Trust and investment services fees
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	47	40
Trust and investment services fees | Consumer Banking
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	47	40
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	2	3
Other banking fees | Consumer Banking
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0	0
Other banking fees | Commercial Banking
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	$ 2	$ 3