Quarterly report pursuant to Section 13 or 15(d)

AVAILABLE-FOR-SALE SECURITIES - Narrative (Details)

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AVAILABLE-FOR-SALE SECURITIES - Narrative (Details) - USD ($)
$ in Millions
3 Months Ended 6 Months Ended
Jun. 30, 2018
Jun. 30, 2017
Jun. 30, 2018
Dec. 31, 2017
Schedule of Available-for-sale Securities [Line Items]        
Pledged investment securities to secure public and trust deposits, trading account liabilities, US Treasury demand notes and security repurchase agreements $ 5,000   $ 5,000 $ 6,000
Commercial        
Schedule of Available-for-sale Securities [Line Items]        
Contractually Specified Servicing Fee, Late Fee, and Ancillary Fee Earned in Exchange for Servicing Financial Asset $ 3 $ 3 $ 6