GOODWILL AND INTANGIBLE ASSETS - Components of Intangible Assets (Details) - USD ($) $ in Millions	Jun. 30, 2018	Dec. 31, 2017
Finite and Indefinite-lived Intangible Assets
Gross carrying amount of Intangible assets (excluding MSRs)	$ 12,003	$ 11,894
Accumulated amortization of Intangible assets (excluding MSRs)	7,274	7,306
Net carrying amount of Intangible assets (excluding MSRs)	4,729	4,588
Gross carrying amount, Mortgage servicing rights (MSRs)	596	558
Mortgage servicing rights (MSRs)	596	558
Gross carrying amount of Intangible assets	12,599	12,452
Accumulated amortization of Intangible assets	7,274	7,306
Total intangible assets	5,325	5,146
Indefinite-lived intangible assets
Finite and Indefinite-lived Intangible Assets
Gross carrying amount of Intangible assets (excluding MSRs)	216	244
Accumulated amortization of Intangible assets (excluding MSRs)	0	0
Net carrying amount of Intangible assets (excluding MSRs)	216	244
Purchased credit card relationships
Finite and Indefinite-lived Intangible Assets
Gross carrying amount of Intangible assets (excluding MSRs)	5,726	5,375
Accumulated amortization of Intangible assets (excluding MSRs)	3,838	3,836
Net carrying amount of Intangible assets (excluding MSRs)	1,888	1,539
Credit card contract related intangibles
Finite and Indefinite-lived Intangible Assets
Gross carrying amount of Intangible assets (excluding MSRs)	5,043	5,045
Accumulated amortization of Intangible assets (excluding MSRs)	2,624	2,456
Net carrying amount of Intangible assets (excluding MSRs)	2,419	2,589
Core deposit intangibles
Finite and Indefinite-lived Intangible Assets
Gross carrying amount of Intangible assets (excluding MSRs)	419	639
Accumulated amortization of Intangible assets (excluding MSRs)	412	628
Net carrying amount of Intangible assets (excluding MSRs)	7	11
Other customer relationships
Finite and Indefinite-lived Intangible Assets
Gross carrying amount of Intangible assets (excluding MSRs)	472	459
Accumulated amortization of Intangible assets (excluding MSRs)	287	272
Net carrying amount of Intangible assets (excluding MSRs)	185	187
Present value of future profits
Finite and Indefinite-lived Intangible Assets
Gross carrying amount of Intangible assets (excluding MSRs)	32	32
Accumulated amortization of Intangible assets (excluding MSRs)	28	28
Net carrying amount of Intangible assets (excluding MSRs)	4	4
Other
Finite and Indefinite-lived Intangible Assets
Gross carrying amount of Intangible assets (excluding MSRs)	95	100
Accumulated amortization of Intangible assets (excluding MSRs)	85	86
Net carrying amount of Intangible assets (excluding MSRs)	$ 10	$ 14