DERIVATIVES ACTIVITIES - Cash Flow Hedges (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Pretax change in accumulated other comprehensive income (loss)
Amount of gain (loss) recognized in AOCI on derivative		$ (356)	$ (173)	$ (150)
Other revenue	[1]	1,504	902	2,163
Net interest revenue	[1]	46,562	45,061	45,476
Cash flow hedges expected to be reclassified within 12 months		$ 404
Maximum length of time hedged in cash flow hedge		10 years
Interest rate contracts
Pretax change in accumulated other comprehensive income (loss)
Amount of gain (loss) recognized in AOCI on derivative		$ (361)	(165)	(219)
Foreign exchange contracts
Pretax change in accumulated other comprehensive income (loss)
Amount of gain (loss) recognized in AOCI on derivative		5	(8)	69
Amount of gain (loss) reclassified from AOCI to earnings | Cash flow hedges
Pretax change in accumulated other comprehensive income (loss)
Other revenue		(17)	(136)	(233)
Net interest revenue		(301)
Amount of gain (loss) reclassified from AOCI to earnings | Cash flow hedges | Interest rate contracts
Pretax change in accumulated other comprehensive income (loss)
Other revenue		0	(126)	(140)
Net interest revenue		(301)
Amount of gain (loss) reclassified from AOCI to earnings | Cash flow hedges | Foreign exchange contracts
Pretax change in accumulated other comprehensive income (loss)
Other revenue		(17)	$ (10)	$ (93)
Net interest revenue		$ 0

[1] Certain prior-period revenue and expense lines and totals were reclassified to conform to the current period’s presentation. See Notes 1 and 3 to the Consolidated Financial Statements.