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