GOODWILL AND INTANGIBLE ASSETS - Changes in Intangible Assets (Details) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2016	Dec. 31, 2015
Finite and Indefinite-lived Intangible Assets
Net carrying amount at December 31, 2015, Intangible assets (excluding MSRs)	$ 3,721
Acquisitions/ divestitures	2,025
Amortization	(424)
Impairments	(1)
FX translation and other	37
Net carrying amount at September 30, 2016, Intangible assets (excluding MSRs)	5,358
Mortgage servicing rights (MSRs)	1,270	$ 1,781
Total intangible assets	6,628	$ 5,502
Indefinite-lived intangible assets
Finite and Indefinite-lived Intangible Assets
Net carrying amount at December 31, 2015, Intangible assets (excluding MSRs)	284
Acquisitions/ divestitures	(18)
Amortization	0
Impairments	(1)
FX translation and other	(37)
Net carrying amount at September 30, 2016, Intangible assets (excluding MSRs)	228
Purchased credit card relationships
Finite and Indefinite-lived Intangible Assets
Net carrying amount at December 31, 2015, Intangible assets (excluding MSRs)	1,086
Acquisitions/ divestitures	848
Amortization	(149)
Impairments	0
FX translation and other	15
Net carrying amount at September 30, 2016, Intangible assets (excluding MSRs)	1,800
Credit card contract related intangibles
Finite and Indefinite-lived Intangible Assets
Net carrying amount at December 31, 2015, Intangible assets (excluding MSRs)	1,901
Acquisitions/ divestitures	1,314
Amortization	(227)
Impairments	0
FX translation and other	18
Net carrying amount at September 30, 2016, Intangible assets (excluding MSRs)	3,006
Core deposit intangibles
Finite and Indefinite-lived Intangible Assets
Net carrying amount at December 31, 2015, Intangible assets (excluding MSRs)	81
Acquisitions/ divestitures	(13)
Amortization	(22)
Impairments	0
FX translation and other	(3)
Net carrying amount at September 30, 2016, Intangible assets (excluding MSRs)	43
Other customer relationships
Finite and Indefinite-lived Intangible Assets
Net carrying amount at December 31, 2015, Intangible assets (excluding MSRs)	219
Acquisitions/ divestitures	0
Amortization	(19)
Impairments	0
FX translation and other	38
Net carrying amount at September 30, 2016, Intangible assets (excluding MSRs)	238
Present value of future profits
Finite and Indefinite-lived Intangible Assets
Net carrying amount at December 31, 2015, Intangible assets (excluding MSRs)	6
Acquisitions/ divestitures	0
Amortization	0
Impairments	0
FX translation and other	(1)
Net carrying amount at September 30, 2016, Intangible assets (excluding MSRs)	5
Other
Finite and Indefinite-lived Intangible Assets
Net carrying amount at December 31, 2015, Intangible assets (excluding MSRs)	144
Acquisitions/ divestitures	(106)
Amortization	(7)
Impairments	0
FX translation and other	7
Net carrying amount at September 30, 2016, Intangible assets (excluding MSRs)	$ 38