MORTGAGE BANKING - Changes Related to MSRs (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Valuation allowance for servicing assets:
Valuation charge-offs	$ 0	$ 5
Residential mortgages
MSRs:
Balance as of beginning of period	168	173
Amount capitalized	10	5
Amortization	(8)	(9)
Carrying amount before valuation allowance	170	169
Valuation allowance for servicing assets:
beginning of period	5	9
Valuation charge-offs	0	5
Balance at end of period	5	14
Net carrying value of MSRs	$ 165	$ 155