SECURITIES - Schedule of Investments in Continuous Loss Positions (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2014 Securities	Dec. 31, 2013 Securities
Schedule of Available-for-sale Securities [Line Items]
Securities Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Number of Issues	81	286
Securities Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Fair Value	$ 3,362	$ 13,529
Securities Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Gross Unrealized Loss	(26)	(193)
Securities Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Number of Issues	70	26
Securities Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Fair Value	2,173	510
Securities Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Gross Unrealized Loss	(90)	(39)
Securities Available-for-sale, Continuous Unrealized Loss Position, Number of Issues	151	312
Securities Available-for-sale, Continuous Unrealized Loss Position, Fair Value	5,535	14,039
Securities Available-for-sale, Continuous Unrealized Loss Position, Gross Unrealized Loss	(116)	(232)
State and political subdivisions
Schedule of Available-for-sale Securities [Line Items]
Securities Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Number of Issues	0	1
Securities Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Fair Value	0	10
Securities Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Gross Unrealized Loss	0	(1)
Securities Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Number of Issues	1	0
Securities Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Fair Value	10	0
Securities Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Gross Unrealized Loss	0	0
Securities Available-for-sale, Continuous Unrealized Loss Position, Number of Issues	1	1
Securities Available-for-sale, Continuous Unrealized Loss Position, Fair Value	10	10
Securities Available-for-sale, Continuous Unrealized Loss Position, Gross Unrealized Loss	0	(1)
Federal agencies and U.S. government sponsored entities
Schedule of Available-for-sale Securities [Line Items]
Securities Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Number of Issues	75	263
Securities Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Fair Value	3,282	12,067
Securities Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Gross Unrealized Loss	(24)	(158)
Securities Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Number of Issues	52	7
Securities Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Fair Value	1,766	20
Securities Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Gross Unrealized Loss	(57)	(2)
Securities Available-for-sale, Continuous Unrealized Loss Position, Number of Issues	127	270
Securities Available-for-sale, Continuous Unrealized Loss Position, Fair Value	5,048	12,087
Securities Available-for-sale, Continuous Unrealized Loss Position, Gross Unrealized Loss	(81)	(160)
Other/non-agency
Schedule of Available-for-sale Securities [Line Items]
Securities Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Number of Issues	6	22
Securities Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Fair Value	80	1,452
Securities Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Gross Unrealized Loss	(2)	(34)
Securities Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Number of Issues	17	19
Securities Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Fair Value	397	490
Securities Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Gross Unrealized Loss	(33)	(37)
Securities Available-for-sale, Continuous Unrealized Loss Position, Number of Issues	23	41
Securities Available-for-sale, Continuous Unrealized Loss Position, Fair Value	477	1,942
Securities Available-for-sale, Continuous Unrealized Loss Position, Gross Unrealized Loss	(35)	(71)
Total mortgage-backed securities
Schedule of Available-for-sale Securities [Line Items]
Securities Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Number of Issues	81	285
Securities Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Fair Value	3,362	13,519
Securities Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Gross Unrealized Loss	(26)	(192)
Securities Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Number of Issues	69	26
Securities Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Fair Value	2,163	510
Securities Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Gross Unrealized Loss	(90)	(39)
Securities Available-for-sale, Continuous Unrealized Loss Position, Number of Issues	150	311
Securities Available-for-sale, Continuous Unrealized Loss Position, Fair Value	5,525	14,029
Securities Available-for-sale, Continuous Unrealized Loss Position, Gross Unrealized Loss	$ (116)	$ (231)