RECLASSIFICATIONS OUT OF ACCUMULATED OTHER COMPREHENSIVE INCOME (LOSS) - Reclassifications out of Accumulated Other Comprehensive Income (Details) - USD ($) $ in Millions		3 Months Ended		9 Months Ended
		Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Interest expense		$ (202)	$ (134)	$ (536)	$ (372)
Net securities impairment losses recognized in earnings		(1)	(3)	(6)	(11)
Salaries and employee benefits		(436)	(432)	(1,312)	(1,289)
Income before income tax expense		513	427	1,409	1,120
Income tax expense		165	130	423	357
NET INCOME		348	297	986	763
Amount Reclassified from AOCI
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Income tax expense		0	1	3	10
NET INCOME		0	2	7	17
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]	3	23	23	66
Interest expense	[1]	1	(8)	(2)	(24)
Other income		0	(5)	0	(5)
Income before income tax expense		4	10	21	37
Income tax expense		2	4	8	14
NET INCOME		2	6	13	23
Reclassification of net securities gains (losses) to net income: | Amount Reclassified from AOCI
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Securities gains, net		2	0	9	13
Net securities impairment losses recognized in earnings		(1)	(3)	(6)	(11)
Income before income tax expense		1	(3)	3	2
Income tax expense		0	(1)	1	1
NET INCOME		1	(2)	2	1
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		(5)	(4)	(14)	(12)
Income before income tax expense		(5)	(4)	(14)	(12)
Income tax expense		(2)	(2)	(6)	(5)
NET INCOME		$ (3)	$ (2)	$ (8)	$ (7)

[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.