MORTGAGE BANKING - Changes Related to MSRs (Details) - Residential mortgages - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
MSRs
Balance as of beginning of period	$ 166	$ 177	$ 173	$ 184
Amount capitalized	10	7	20	20
Amortization	(9)	(8)	(26)	(28)
Carrying amount before valuation allowance	167	176	167	176
Valuation allowance for servicing assets
Balance as of beginning of period	13	11	9	18
Valuation charge-offs (recoveries)	2	1	6	(6)
Balance at end of period	15	12	15	12
Net carrying value of MSRs	$ 152	$ 164	$ 152	$ 164