RECLASSIFICATIONS OUT OF ACCUMULATED OTHER COMPREHENSIVE INCOME (LOSS) - Reclassifications out of Accumulated Other Comprehensive Income (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Interest expense		$ (508)	$ (452)	$ (363)
Net securities impairment losses recognized in earnings		(12)	(7)	(10)
Salaries and employee benefits		(1,709)	(1,636)	(1,678)
Income before income tax expense		1,534	1,263	1,268
Income tax expense		489	423	403
NET INCOME		1,045	840	865
Amount Reclassified from AOCI
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Income tax expense		38	17	71
NET INCOME		63	20	112
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]	90	82	72
Interest expense	[1]	(27)	(59)	(99)
Other income		(5)	0	0
Income before income tax expense		58	23	(27)
Income tax expense		22	9	(10)
NET INCOME		36	14	(17)
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		16	29	28
Net securities impairment losses recognized in earnings		(12)	(7)	(10)
Income before income tax expense		4	22	18
Income tax expense		2	8	7
NET INCOME		2	14	11
Reclassification of changes related to employee benefit plans: | Amount Reclassified from AOCI
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Salaries and employee benefits		39	(8)	192
Income before income tax expense		39	(8)	192
Income tax expense		14	0	74
NET INCOME		$ 25	$ (8)	$ 118

[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 expense of the underlying hedged item.