MORTGAGE BANKING - Changes Related to MSRs (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Valuation allowance for servicing assets:
Valuation recoveries			$ (3)	$ (1)
Residential mortgages
MSRs:
Balance as of beginning of period	$ 201	$ 170	201	168
Amount capitalized	8	8	15	18
Servicing Asset at Amortized Cost, Additions	16	0	16	0
Amortization	(8)	(8)	(15)	(16)
Carrying amount before valuation allowance	217	170	217	170
Valuation allowance for servicing assets:
Balance at beginning of period	0	5	3	5
Valuation recoveries	0	(1)	(3)	(1)
Balance at end of period	0	4	0	4
Net carrying value of MSRs	$ 217	$ 166	$ 217	$ 166