FAIR VALUE MEASUREMENTS - Schedule of Assets Measured on Recurring Basis Level 3 Rollforward (Details) - Residential mortgages - USD ($) $ in Millions		3 Months Ended	9 Months Ended
		Sep. 30, 2018	Sep. 30, 2018
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance		$ 0	$ 0
Acquired MSRs		590	590
Amount capitalized		29	29
Change in unpaid principal balance during the period	[1]	(12)	(12)
Change in fair value during the period	[2]	5	5
Ending balance		$ 612	$ 612

[1] Represents changes in value of the MSRs 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.

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