GOODWILL AND INTANGIBLE ASSETS - Intangible Assets (Details) - USD ($) $ in Millions	6 Months Ended
	Jun. 30, 2022	Dec. 31, 2021
Finite-Lived Intangible Assets, Net [Abstract]
Gross	$ 261	$ 97
Accumulated Amortization	50	33
Net	$ 211	64
Core deposits
Finite-Lived Intangible Assets [Line Items]
Amortizable Lives	10 years
Finite-Lived Intangible Assets, Net [Abstract]
Gross	$ 144	0
Accumulated Amortization	7	0
Net	137	0
Core deposits | Investors Acquisition
Finite-Lived Intangible Assets, Net [Abstract]
Gross	97
Core deposits | 80 Branches and Deposit Business, HSBC Bank
Finite-Lived Intangible Assets, Net [Abstract]
Gross	47
Acquired technology
Finite-Lived Intangible Assets, Net [Abstract]
Gross	21	21
Accumulated Amortization	15	11
Net	6	10
Acquired relationships
Finite-Lived Intangible Assets, Net [Abstract]
Gross	53	53
Accumulated Amortization	17	14
Net	36	39
Naming rights
Finite-Lived Intangible Assets, Net [Abstract]
Gross	31	10
Accumulated Amortization	5	3
Net	26	7
Naming rights | Investors Acquisition
Finite-Lived Intangible Assets, Net [Abstract]
Gross	22
Other
Finite-Lived Intangible Assets, Net [Abstract]
Gross	12	13
Accumulated Amortization	6	5
Net	$ 6	$ 8
Minimum | Acquired technology
Finite-Lived Intangible Assets [Line Items]
Amortizable Lives	5 years
Minimum | Acquired relationships
Finite-Lived Intangible Assets [Line Items]
Amortizable Lives	2 years
Minimum | Naming rights
Finite-Lived Intangible Assets [Line Items]
Amortizable Lives	5 years
Minimum | Other
Finite-Lived Intangible Assets [Line Items]
Amortizable Lives	2 years
Maximum | Acquired technology
Finite-Lived Intangible Assets [Line Items]
Amortizable Lives	7 years
Maximum | Acquired relationships
Finite-Lived Intangible Assets [Line Items]
Amortizable Lives	15 years
Maximum | Naming rights
Finite-Lived Intangible Assets [Line Items]
Amortizable Lives	10 years
Maximum | Other
Finite-Lived Intangible Assets [Line Items]
Amortizable Lives	7 years