GOODWILL AND INTANGIBLE ASSETS - Changes in Intangible Assets (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Finite and Indefinite-lived Intangible Assets
Net carrying amount of intangible assets (excluding MSRs), beginning balance	$ 4,636
Mortgage servicing rights (MSRs), beginning balance	584
Net carrying amount of intangible assets, beginning balance	5,220
Acquisitions/ divestitures	92
Amortization	(564)
Impairments	0
FX translation and other	163
Net carrying amount of intangible assets (excluding MSRs), ending balance	4,327	$ 4,636
Mortgage servicing rights (MSRs), ending balance	495	584
Net carrying amount of intangible assets, ending balance	4,822	5,220
Purchased credit card relationships
Finite and Indefinite-lived Intangible Assets
Net carrying amount of intangible assets (excluding MSRs), beginning balance	1,797
Acquisitions/ divestitures	9
Amortization	(189)
Impairments	0
FX translation and other	0
Net carrying amount of intangible assets (excluding MSRs), ending balance	1,617	1,797
Credit card contract related intangibles
Finite and Indefinite-lived Intangible Assets
Net carrying amount of intangible assets (excluding MSRs), beginning balance	2,434
Acquisitions/ divestitures	73
Amortization	(336)
Impairments	0
FX translation and other	153
Net carrying amount of intangible assets (excluding MSRs), ending balance	2,324	2,434
Core deposit intangibles
Finite and Indefinite-lived Intangible Assets
Net carrying amount of intangible assets (excluding MSRs), beginning balance	4
Acquisitions/ divestitures	0
Amortization	(4)
Impairments	0
FX translation and other	1
Net carrying amount of intangible assets (excluding MSRs), ending balance	1	4
Other customer relationships
Finite and Indefinite-lived Intangible Assets
Net carrying amount of intangible assets (excluding MSRs), beginning balance	171
Acquisitions/ divestitures	0
Amortization	(24)
Impairments	0
FX translation and other	2
Net carrying amount of intangible assets (excluding MSRs), ending balance	149	171
Present value of future profits
Finite and Indefinite-lived Intangible Assets
Net carrying amount of intangible assets (excluding MSRs), beginning balance	3
Acquisitions/ divestitures	0
Amortization	0
Impairments	0
FX translation and other	0
Net carrying amount of intangible assets (excluding MSRs), ending balance	3	3
Other
Finite and Indefinite-lived Intangible Assets
Net carrying amount of intangible assets (excluding MSRs), beginning balance	9
Acquisitions/ divestitures	6
Amortization	(11)
Impairments	0
FX translation and other	1
Net carrying amount of intangible assets (excluding MSRs), ending balance	5	9
Indefinite-lived intangible assets
Finite and Indefinite-lived Intangible Assets
Net carrying amount of intangible assets (excluding MSRs), beginning balance	218
Acquisitions/ divestitures	4
Amortization	0
Impairments	0
FX translation and other	6
Net carrying amount of intangible assets (excluding MSRs), ending balance	$ 228	$ 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	96.00%	96.00%