GOODWILL AND INTANGIBLE ASSETS - Components of Intangible Assets (Details) - USD ($) $ in Millions	Sep. 30, 2023	Dec. 31, 2022
Finite and Indefinite-lived Intangible Assets
Gross carrying amount of Intangible assets (excluding MSRs)	$ 10,096	$ 10,078
Accumulated amortization of Intangible assets (excluding MSRs)	6,285	6,315
Net carrying amount of Intangible assets (excluding MSRs)	3,811	3,763
Gross carrying amount, Mortgage servicing rights (MSRs)	729	665
Mortgage servicing rights (MSRs)	729	665
Gross carrying amount of Intangible assets	10,825	10,743
Accumulated amortization of Intangible assets	6,285	6,315
Total intangible assets	4,540	4,428
Indefinite-lived intangible assets
Finite and Indefinite-lived Intangible Assets
Gross carrying amount of Intangible assets (excluding MSRs)	234	192
Net carrying amount of Intangible assets (excluding MSRs)	234	192
Purchased credit card relationships
Finite and Indefinite-lived Intangible Assets
Gross carrying amount of Intangible assets (excluding MSRs)	5,302	5,513
Accumulated amortization of Intangible assets (excluding MSRs)	4,328	4,426
Net carrying amount of Intangible assets (excluding MSRs)	974	1,087
Credit card contract related intangibles
Finite and Indefinite-lived Intangible Assets
Gross carrying amount of Intangible assets (excluding MSRs)	4,178	3,903
Accumulated amortization of Intangible assets (excluding MSRs)	1,652	1,518
Net carrying amount of Intangible assets (excluding MSRs)	2,526	2,385
Other customer relationships
Finite and Indefinite-lived Intangible Assets
Gross carrying amount of Intangible assets (excluding MSRs)	346	373
Accumulated amortization of Intangible assets (excluding MSRs)	270	283
Net carrying amount of Intangible assets (excluding MSRs)	76	90
Present value of future profits
Finite and Indefinite-lived Intangible Assets
Gross carrying amount of Intangible assets (excluding MSRs)	36	32
Accumulated amortization of Intangible assets (excluding MSRs)	35	31
Net carrying amount of Intangible assets (excluding MSRs)	1	1
Other
Finite and Indefinite-lived Intangible Assets
Gross carrying amount of Intangible assets (excluding MSRs)	0	65
Accumulated amortization of Intangible assets (excluding MSRs)	0	57
Net carrying amount of Intangible assets (excluding MSRs)	$ 0	$ 8