RECLASSIFICATIONS OUT OF ACCUMULATED OTHER COMPREHENSIVE LOSS - Reclassifications out of Accumulated Other Comprehensive Income (Details) - USD ($) $ in Millions		3 Months Ended
		Mar. 31, 2018	Mar. 31, 2017
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Interest expense		$ (237)	$ (155)
Net debt securities impairment losses recognized in earnings		(1)	(1)
Other operating expense		(470)	(446)
Income before income tax expense		501	434
Income tax expense		113	114
NET INCOME		388	320
Amount Reclassified from AOCI
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Income tax expense		1	3
NET INCOME		0	5
Reclassification adjustment for net derivative (losses) gains included in net income: | Amount Reclassified from AOCI
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Interest income	[1]	(6)	12
Interest expense	[1]	4	(2)
Income before income tax expense		(2)	10
Income tax expense		0	4
NET INCOME		(2)	6
Reclassification of net debt securities gains (losses) to net income: | Amount Reclassified from AOCI
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Securities gains, net		8	4
Net debt securities impairment losses recognized in earnings		(1)	(1)
Income before income tax expense		7	3
Income tax expense		2	1
NET INCOME		5	2
Reclassification of changes related to the employee benefit plan: | Amount Reclassified from AOCI
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Other operating expense		(4)	(5)
Income before income tax expense		(4)	(5)
Income tax expense		(1)	(2)
NET INCOME		$ (3)	$ (3)

[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.