RECLASSIFICATIONS OUT OF ACCUMULATED OTHER COMPREHENSIVE INCOME - Effects to Net Income of Amounts Reclassified Out of OCI (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Net interest income	$ 3,301	$ 3,058	$ 3,227
Provision for credit losses	319	479	413
Noninterest income	1,678	1,632	1,667
Noninterest expense	3,392	7,679	3,457
Income (loss) before income tax expense (benefit)	1,268	(3,468)	1,024
Income tax expense (benefit)	403	(42)	381
NET INCOME (LOSS)	865	(3,426)	643
Amount Reclassified from OCI
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Net interest income	3,301	3,058	3,227
Provision for credit losses	319	479	413
Noninterest income	1,678	1,632	1,667
Noninterest expense	3,392	7,679	3,457
Income (loss) before income tax expense (benefit)	1,268	(3,468)	1,024
Income tax expense (benefit)	403	(42)	381
NET INCOME (LOSS)	865	(3,426)	643
Amount Reclassified from AOCI
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Net interest income	(27)	(179)	(335)
Noninterest income	18	135	71
Noninterest expense	(192)	190	(40)
Income tax expense (benefit)	71	(87)	82
NET INCOME (LOSS)	112	(147)	(142)
Net Unrealized Gains (Losses) on Derivatives | Amount Reclassified from AOCI
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Income (loss) before income tax expense (benefit)	(27)	(180)	(335)
Income tax expense (benefit)	(10)	(66)	(123)
NET INCOME (LOSS)	$ (17)	$ (114)	$ (212)