MORTGAGE BANKING - Changes Related to MSR's - Fair Value Method (Details) $ in Millions	12 Months Ended
	Dec. 31, 2018 USD ($)
MSRs:
Fair value at end of the period	$ 600
Residential mortgages
MSRs:
Fair value as of beginning of the period	0
Acquired MSRs	590
Amounts capitalized	73
Changes in unpaid principal balance during the period	(32)	[1]
Changes in fair value during the period	(31)	[2]
Fair value at end of the period	$ 600

[1] Represents changes in value due to i) passage of time including the impact from both regularly scheduled loan principal payments and partial paydowns, and ii) loans that paid off during the period.

[2] Represents changes in value primarily due to market driven changes in interest rates and prepayment speeds.