SECURITIES - Schedule of Investments in Continuous Loss Positions (Details) $ in Millions	Mar. 31, 2019 USD ($) Securities	Dec. 31, 2018 USD ($) Securities
Number of Issues
Less than 12 Months | Securities	13	176
12 Months or Longer | Securities	526	440
Total | Securities	539	616
Fair Value
Less than 12 Months	$ 569	$ 5,020
12 Months or Longer	17,596	15,196
Total	18,165	20,216
Gross Unrealized Losses
Less than 12 Months	(1)	(90)
12 Months or Longer	(419)	(654)
Total	$ (420)	$ (744)
Federal agencies and U.S. government sponsored entities
Number of Issues
Less than 12 Months | Securities	13	166
12 Months or Longer | Securities	519	429
Total | Securities	532	595
Fair Value
Less than 12 Months	$ 569	$ 4,881
12 Months or Longer	17,548	15,124
Total	18,117	20,005
Gross Unrealized Losses
Less than 12 Months	(1)	(89)
12 Months or Longer	(415)	(648)
Total	$ (416)	$ (737)
Other/non-agency
Number of Issues
Less than 12 Months | Securities	0	10
12 Months or Longer | Securities	7	11
Total | Securities	7	21
Fair Value
Less than 12 Months	$ 0	$ 139
12 Months or Longer	48	72
Total	48	211
Gross Unrealized Losses
Less than 12 Months	0	(1)
12 Months or Longer	(4)	(6)
Total	$ (4)	$ (7)