SECURITIES - Schedule of Investments in Continuous Loss Positions (Details) $ in Millions	Sep. 30, 2018 USD ($) Securities	Dec. 31, 2017 USD ($) Securities
Number of Issues
Less than 12 Months | Securities	507	300
12 Months or Longer | Securities	170	162
Total | Securities	677	462
Fair Value
Less than 12 Months	$ 15,719	$ 10,218
12 Months or Longer	7,291	8,145
Total	23,010	18,363
Gross Unrealized Losses
Less than 12 Months	(520)	(98)
12 Months or Longer	(494)	(232)
Total	$ (1,014)	$ (330)
Federal agencies and U.S. government sponsored entities
Number of Issues
Less than 12 Months | Securities	493	294
12 Months or Longer | Securities	159	152
Total | Securities	652	446
Fair Value
Less than 12 Months	$ 15,177	$ 10,163
12 Months or Longer	7,215	8,061
Total	22,392	18,224
Gross Unrealized Losses
Less than 12 Months	(514)	(97)
12 Months or Longer	(488)	(226)
Total	$ (1,002)	$ (323)
Other/non-agency
Number of Issues
Less than 12 Months | Securities	14	6
12 Months or Longer | Securities	11	10
Total | Securities	25	16
Fair Value
Less than 12 Months	$ 542	$ 55
12 Months or Longer	76	84
Total	618	139
Gross Unrealized Losses
Less than 12 Months	(6)	(1)
12 Months or Longer	(6)	(6)
Total	$ (12)	$ (7)