GOODWILL AND INTANGIBLE ASSETS - Changes in Intangible Assets (Details) $ in Millions	12 Months Ended
	Dec. 31, 2018 USD ($)
Finite and Indefinite-lived Intangible Assets
Net carrying amount of intangible assets (excluding MSRs), beginning balance	$ 4,588
Mortgage servicing rights (MSRs), beginning balance	558
Net carrying amount of intangible assets, beginning balance	5,146
Acquisitions/ divestitures	614
Amortization	(557)
FX translation and other	(9)
Net carrying amount of intangible assets (excluding MSRs), ending balance	4,636
Mortgage servicing rights (MSRs), ending balance	584
Net carrying amount of intangible assets, ending balance	5,220
Purchased credit card relationships
Finite and Indefinite-lived Intangible Assets
Net carrying amount of intangible assets (excluding MSRs), beginning balance	1,539
Acquisitions/ divestitures	429
Amortization	(173)
FX translation and other	2
Net carrying amount of intangible assets (excluding MSRs), ending balance	1,797
Credit card contract related intangibles
Finite and Indefinite-lived Intangible Assets
Net carrying amount of intangible assets (excluding MSRs), beginning balance	2,589
Acquisitions/ divestitures	185
Amortization	(339)
FX translation and other	(1)
Net carrying amount of intangible assets (excluding MSRs), ending balance	2,434
Core deposit intangibles
Finite and Indefinite-lived Intangible Assets
Net carrying amount of intangible assets (excluding MSRs), beginning balance	11
Acquisitions/ divestitures	0
Amortization	(8)
FX translation and other	1
Net carrying amount of intangible assets (excluding MSRs), ending balance	4
Other customer relationships
Finite and Indefinite-lived Intangible Assets
Net carrying amount of intangible assets (excluding MSRs), beginning balance	187
Acquisitions/ divestitures	0
Amortization	(25)
FX translation and other	9
Net carrying amount of intangible assets (excluding MSRs), ending balance	171
Present value of future profits
Finite and Indefinite-lived Intangible Assets
Net carrying amount of intangible assets (excluding MSRs), beginning balance	4
Acquisitions/ divestitures	0
Amortization	0
FX translation and other	(1)
Net carrying amount of intangible assets (excluding MSRs), ending balance	3
Other
Finite and Indefinite-lived Intangible Assets
Net carrying amount of intangible assets (excluding MSRs), beginning balance	14
Acquisitions/ divestitures	0
Amortization	(12)
FX translation and other	7
Net carrying amount of intangible assets (excluding MSRs), ending balance	9
Indefinite-lived intangible assets
Finite and Indefinite-lived Intangible Assets
Net carrying amount of intangible assets (excluding MSRs), beginning balance	244
Acquisitions/ divestitures	0
Amortization	0
FX translation and other	(26)
Net carrying amount of intangible assets (excluding MSRs), ending balance	$ 218
Intangible Assets, Excluding Mortgage Servicing Rights | Customer Concentration Risk | American Airlines, Sears, The Home Depot and Costco | Credit card contract related intangibles
Finite and Indefinite-lived Intangible Assets
Intangible assets, percent	97.00%