Amount of operating interest income, including amortization and accretion of premiums and discounts, on securities subject to state, federal and other income tax.

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SECURITIES - Narrative (Details) - USD ($) $ in Millions	3 Months Ended
SECURITIES - Narrative (Details) - USD ($) $ in Millions	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017	Dec. 31, 2016
Schedule of Available-for-sale Securities [Line Items]
Taxable interest income from securities	$ 168	$ 160
Impaired debt securities sold	0	0
Mortgage-backed securities
Schedule of Available-for-sale Securities [Line Items]
Securitizations of mortgage loans	26	22
Available-for-sale Securities
Schedule of Available-for-sale Securities [Line Items]
Cumulative credit losses recognized in earnings	80	75	$ 80	$ 75
OTTI in earnings	1	1
Held-to-maturity Securities
Schedule of Available-for-sale Securities [Line Items]
Cumulative credit losses recognized in earnings	$ 0	$ 0