MORTGAGE BANKING - Narrative (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Accounts, Notes, Loans and Financing Receivable [Line Items]
Proceeds from sale of residential mortgages	$ 2,652	$ 2,381	$ 1,578
Repurchased mortgage loans	6	10	25
Mortgage servicing fees	51	55	59
Mortgage servicing rights valuation recovery	4	9	5
Residential mortgages
Accounts, Notes, Loans and Financing Receivable [Line Items]
Proceeds from sale of residential mortgages	2,700	2,700	1,600
Gain on sale of residential mortgages	$ 69	$ 51	$ 36
Minimum
Accounts, Notes, Loans and Financing Receivable [Line Items]
Adverse change in basis points	0.50%	0.50%
Maximum
Accounts, Notes, Loans and Financing Receivable [Line Items]
Adverse change in basis points	1.00%	1.00%