RECLASSIFICATIONS OUT OF ACCUMULATED OTHER COMPREHENSIVE INCOME (LOSS) - Effects to Net Income of Amounts Reclassified Out of OCI (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Net interest income	$ 3,402	$ 3,301	$ 3,058
Provision for credit losses	302	319	479
Noninterest income	1,422	1,678	1,632
Noninterest expense	3,259	3,392	7,679
Income (loss) before income tax expense (benefit)	1,263	1,268	(3,468)
Income tax expense (benefit)	423	403	(42)
NET INCOME (LOSS)	840	865	(3,426)
Amount Reclassified from OCI
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Net interest income	3,402	3,301	3,058
Provision for credit losses	302	319	479
Noninterest income	1,422	1,678	1,632
Noninterest expense	3,259	3,392	7,679
Income (loss) before income tax expense (benefit)	1,263	1,268	(3,468)
Income tax expense (benefit)	423	403	(42)
NET INCOME (LOSS)	840	865	(3,426)
Amount Reclassified from AOCI
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Net interest income	23	(27)	(179)
Noninterest income	22	18	135
Noninterest expense	8	(192)	190
Income tax expense (benefit)	17	71	(87)
NET INCOME (LOSS)	$ 20	$ 112	$ (147)