SECURITIES - Schedule of Investments in Continuous Loss Positions (Details) $ in Millions	Mar. 31, 2018 USD ($) Securities	Dec. 31, 2017 USD ($) Securities
Number of Issues
Less than 12 Months | Securities	423	300
12 Months or Longer | Securities	164	162
Total | Securities	587	462
Fair Value
Less than 12 Months	$ 14,695	$ 10,218
12 Months or Longer	7,704	8,145
Total	22,399	18,363
Gross Unrealized Losses
Less than 12 Months	(355)	(98)
12 Months or Longer	(400)	(232)
Total	$ (755)	$ (330)
Federal agencies and U.S. government sponsored entities
Number of Issues
Less than 12 Months | Securities	414	294
12 Months or Longer | Securities	154	152
Total | Securities	568	446
Fair Value
Less than 12 Months	$ 14,541	$ 10,163
12 Months or Longer	7,624	8,061
Total	22,165	18,224
Gross Unrealized Losses
Less than 12 Months	(352)	(97)
12 Months or Longer	(395)	(226)
Total	$ (747)	$ (323)
Other/non-agency
Number of Issues
Less than 12 Months | Securities	9	6
12 Months or Longer | Securities	10	10
Total | Securities	19	16
Fair Value
Less than 12 Months	$ 154	$ 55
12 Months or Longer	80	84
Total	234	139
Gross Unrealized Losses
Less than 12 Months	(3)	(1)
12 Months or Longer	(5)	(6)
Total	$ (8)	$ (7)