SECURITIES - Schedule of Investments in Continuous Loss Positions (Details) $ in Millions	Jun. 30, 2017 USD ($) Securities	Dec. 31, 2016 USD ($) Securities
Number of Issues
Less than 12 Months | Securities	301	328
12 Months or Longer | Securities	36	45
Total | Securities	337	373
Fair Value
Less than 12 Months	$ 13,613	$ 15,403
12 Months or Longer	577	763
Total	14,190	16,166
Gross Unrealized Losses
Less than 12 Months	(219)	(292)
12 Months or Longer	(21)	(44)
Total	$ (240)	$ (336)
State and political subdivisions
Number of Issues
Less than 12 Months | Securities	0	1
12 Months or Longer | Securities	0	0
Total | Securities	0	1
Fair Value
Less than 12 Months	$ 0	$ 8
12 Months or Longer	0	0
Total	0	8
Gross Unrealized Losses
Less than 12 Months	0	0
12 Months or Longer	0	0
Total	$ 0	$ 0
Federal agencies and U.S. government sponsored entities
Number of Issues
Less than 12 Months | Securities	301	323
12 Months or Longer | Securities	24	25
Total | Securities	325	348
Fair Value
Less than 12 Months	$ 13,613	$ 15,387
12 Months or Longer	423	461
Total	14,036	15,848
Gross Unrealized Losses
Less than 12 Months	(219)	(292)
12 Months or Longer	(12)	(16)
Total	$ (231)	$ (308)
Other/non-agency
Number of Issues
Less than 12 Months | Securities	0	4
12 Months or Longer | Securities	12	20
Total | Securities	12	24
Fair Value
Less than 12 Months	$ 0	$ 8
12 Months or Longer	154	302
Total	154	310
Gross Unrealized Losses
Less than 12 Months	0	0
12 Months or Longer	(9)	(28)
Total	$ (9)	$ (28)
Total mortgage-backed securities
Number of Issues
Less than 12 Months | Securities	301	327
12 Months or Longer | Securities	36	45
Total | Securities	337	372
Fair Value
Less than 12 Months	$ 13,613	$ 15,395
12 Months or Longer	577	763
Total	14,190	16,158
Gross Unrealized Losses
Less than 12 Months	(219)	(292)
12 Months or Longer	(21)	(44)
Total	$ (240)	$ (336)