DERIVATIVE FINANCIAL INSTRUMENTS - MSR Hedging Activities (Details) - USD ($) $ in Millions	Sep. 30, 2018	Dec. 31, 2017
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Derivative, Notional Amount	$ 5,727	$ 8,375

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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