RECLASSIFICATIONS OUT OF ACCUMULATED OTHER COMPREHENSIVE LOSS - Reclassifications out of Accumulated Other Comprehensive Loss (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Interest expense		$ (747)	$ (508)	$ (452)
Net securities impairment losses recognized in earnings		(7)	(12)	(7)
Salaries and employee benefits		(1,761)	(1,709)	(1,636)
Income before income tax expense		1,912	1,534	1,263
Income tax expense		260	489	423
NET INCOME		1,652	1,045	840
Amount Reclassified from AOCI
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Income tax expense		(6)	38	17
NET INCOME		(13)	63	20
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]	25	90	82
Interest expense	[1]	0	(27)	(59)
Other income		0	(5)	0
Income before income tax expense		25	58	23
Income tax expense		9	22	9
NET INCOME		16	36	14
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		11	16	29
Net securities impairment losses recognized in earnings		(7)	(12)	(7)
Income before income tax expense		4	4	22
Income tax expense		2	2	8
NET INCOME		2	2	14
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		(48)	39	(8)
Income before income tax expense		(48)	39	(8)
Income tax expense		(17)	14	0
NET INCOME		$ (31)	$ 25	$ (8)

[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.