SECURITIES - Schedule of Investments in Continuous Loss Positions (Details) $ in Millions	Jun. 30, 2018 USD ($) Securities	Dec. 31, 2017 USD ($) Securities
Number of Issues
Less than 12 Months | Securities	445	300
12 Months or Longer | Securities	165	162
Total | Securities	610	462
Fair Value
Less than 12 Months	$ 14,669	$ 10,218
12 Months or Longer	7,434	8,145
Total	22,103	18,363
Gross Unrealized Losses
Less than 12 Months	(437)	(98)
12 Months or Longer	(436)	(232)
Total	$ (873)	$ (330)
Federal agencies and U.S. government sponsored entities
Number of Issues
Less than 12 Months | Securities	434	294
12 Months or Longer | Securities	155	152
Total | Securities	589	446
Fair Value
Less than 12 Months	$ 14,384	$ 10,163
12 Months or Longer	7,358	8,061
Total	21,742	18,224
Gross Unrealized Losses
Less than 12 Months	(434)	(97)
12 Months or Longer	(430)	(226)
Total	$ (864)	$ (323)
Other/non-agency
Number of Issues
Less than 12 Months | Securities	11	6
12 Months or Longer | Securities	10	10
Total | Securities	21	16
Fair Value
Less than 12 Months	$ 285	$ 55
12 Months or Longer	76	84
Total	361	139
Gross Unrealized Losses
Less than 12 Months	(3)	(1)
12 Months or Longer	(6)	(6)
Total	$ (9)	$ (7)