NONINTEREST INCOME - Components of Revenue from Contracts with Customers (Details) - USD ($) $ in Millions		3 Months Ended	9 Months Ended
		Sep. 30, 2018	Sep. 30, 2018
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	[1]	$ 285	$ 833
Consumer Banking
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers		201	585
Commercial Banking
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers		84	248
Service charges and fees
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	[1]	131	382
Service charges and fees | Consumer Banking
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers		105	303
Service charges and fees | Commercial Banking
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers		26	79
Card fees
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	[1]	61	182
Card fees | Consumer Banking
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers		51	154
Card fees | Commercial Banking
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers		10	28
Capital markets fees
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	[1]	46	134
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		46	134
Trust and investment services fees
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	[1]	45	128
Trust and investment services fees | Consumer Banking
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers		45	128
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	[1]	2	7
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	$ 7

[1] There is no revenue from contracts with customers included in Other non-segment operations.