MORTGAGE BANKING - Changes Related to MSRs (Details) - Residential mortgages - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
MSRs
Balance as of beginning of period	$ 169	$ 180	$ 173	$ 184
Amount capitalized	5	7	10	13
Amortization	(8)	(10)	(17)	(20)
Carrying amount before valuation allowance	166	177	166	177
Valuation allowance for servicing assets
Balance as of beginning of period	14	17	9	18
Valuation charge-offs (recoveries)	(1)	(6)	4	(7)
Balance at end of period	13	11	13	11
Net carrying value of MSRs	$ 153	$ 166	$ 153	$ 166