RECLASSIFICATIONS OUT OF ACCUMULATED OTHER COMPREHENSIVE INCOME (LOSS) - Reclassifications out of Accumulated Other Comprehensive Income (Details) - USD ($) $ in Millions		3 Months Ended		6 Months Ended
		Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Interest expense		$ (179)	$ (123)	$ (334)	$ (238)
Net securities impairment losses recognized in earnings		(4)	(7)	(5)	(8)
Salaries and employee benefits		(432)	(432)	(876)	(857)
Income before income tax expense		462	361	896	693
Income tax expense		144	118	258	227
NET INCOME		318	243	638	466
Amount Reclassified from AOCI
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Income tax expense		0	2	3	9
NET INCOME		2	4	7	15
Reclassification adjustment for net derivative gains (losses) included in net income: | Amount Reclassified from AOCI
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Interest income	[1]	8	21	20	43
Interest expense	[1]	(1)	(8)	(3)	(16)
Income before income tax expense		7	13	17	27
Income tax expense		2	4	6	10
NET INCOME		5	9	11	17
Reclassification of net securities gains (losses) to net income (loss): | Amount Reclassified from AOCI
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Securities gains, net		3	4	7	13
Net securities impairment losses recognized in earnings		(4)	(7)	(5)	(8)
Income before income tax expense		(1)	(3)	2	5
Income tax expense		0	(1)	1	2
NET INCOME		(1)	(2)	1	3
Reclassification of changes related to the employee benefit plan: | Amount Reclassified from AOCI
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Salaries and employee benefits		(4)	(4)	(9)	(8)
Income before income tax expense		(4)	(4)	(9)	(8)
Income tax expense		(2)	(1)	(4)	(3)
NET INCOME		$ (2)	$ (3)	$ (5)	$ (5)

[1] This amount includes both (a) the amortization of effective gains and losses associated with the Company’s terminated cash flow hedges and (b) the current reporting period’s interest settlements realized on the Company’s active cash flow hedges. Both (a) and (b) were previously included on the accumulated other comprehensive loss line item on the Consolidated Balance Sheets and were subsequently recorded as adjustments to the interest income or expense of the underlying hedged item.