Quarterly report pursuant to Section 13 or 15(d)

LOAN SALES AND SECURITIZATIONS - Narrative (Details)

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LOAN SALES AND SECURITIZATIONS - Narrative (Details) - Residential Mortgage - USD ($)
$ in Millions
3 Months Ended 9 Months Ended 12 Months Ended
Sep. 30, 2018
Sep. 30, 2017
Sep. 30, 2018
Dec. 31, 2017
Servicing Assets at Fair Value [Line Items]        
Servicing income $ 15 $ 14 $ 44 $ 42
Unpaid principal balance of third party serviced loans $ 20,600   $ 20,600 $ 19,800