MORTGAGE BANKING - Narrative (Details) - USD ($) $ in Millions	9 Months Ended		21 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015
Accounts, Notes, Loans and Financing Receivable [Line Items]
Proceeds from sale of residential mortgages	$ 1,780	$ 1,089
Repurchased mortgage loans	9	22	$ 34
Mortgage servicing fees	41	44
Mortgage servicing rights valuation recovery	(6)	(8)
Residential mortgages
Accounts, Notes, Loans and Financing Receivable [Line Items]
Proceeds from sale of residential mortgages	1,500	1,100
Gain on sale of residential mortgages	$ 43	$ 25