LOANS AND LEASES - Schedule of Loans Modified, Past Due (Details) - USD ($) $ in Millions	Mar. 31, 2025	Mar. 31, 2024
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans and leases	$ 750	$ 696
Current
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans and leases	696	611
30-59 Days Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans and leases	20	49
60-89 Days Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans and leases	3	2
90 Days or Greater
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans and leases	31	34
Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans and leases	513	501
Commercial | Current
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans and leases	470	451
Commercial | 30-59 Days Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans and leases	16	46
Commercial | 60-89 Days Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans and leases	2	2
Commercial | 90 Days or Greater
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans and leases	25	2
Commercial | Commercial construction
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans and leases	25	4
Commercial | Commercial construction | Current
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans and leases	25	4
Commercial | Commercial construction | 30-59 Days Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans and leases	0	0
Commercial | Commercial construction | 60-89 Days Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans and leases	0	0
Commercial | Commercial construction | 90 Days or Greater
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans and leases	0	0
Commercial | Owner occupied commercial mortgage
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans and leases	65	29
Commercial | Owner occupied commercial mortgage | Current
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans and leases	61	26
Commercial | Owner occupied commercial mortgage | 30-59 Days Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans and leases	3	2
Commercial | Owner occupied commercial mortgage | 60-89 Days Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans and leases	1	0
Commercial | Owner occupied commercial mortgage | 90 Days or Greater
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans and leases	0	1
Commercial | Non-owner occupied commercial mortgage
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans and leases	236	353
Commercial | Non-owner occupied commercial mortgage | Current
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans and leases	204	314
Commercial | Non-owner occupied commercial mortgage | 30-59 Days Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans and leases	9	39
Commercial | Non-owner occupied commercial mortgage | 60-89 Days Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans and leases	0	0
Commercial | Non-owner occupied commercial mortgage | 90 Days or Greater
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans and leases	23	0
Commercial | Commercial and industrial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans and leases	187	115
Commercial | Commercial and industrial | Current
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans and leases	180	107
Commercial | Commercial and industrial | 30-59 Days Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans and leases	4	5
Commercial | Commercial and industrial | 60-89 Days Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans and leases	1	2
Commercial | Commercial and industrial | 90 Days or Greater
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans and leases	2	1
Consumer
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans and leases	25	21
Consumer | Current
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans and leases	20	19
Consumer | 30-59 Days Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans and leases	1	1
Consumer | 60-89 Days Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans and leases	1	0
Consumer | 90 Days or Greater
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans and leases	3	1
Consumer | Residential mortgage
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans and leases	17	17
Consumer | Residential mortgage | Current
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans and leases	12	15
Consumer | Residential mortgage | 30-59 Days Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans and leases	1	1
Consumer | Residential mortgage | 60-89 Days Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans and leases	1	0
Consumer | Residential mortgage | 90 Days or Greater
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans and leases	3	1
Consumer | Revolving mortgage
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans and leases	8	4
Consumer | Revolving mortgage | Current
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans and leases	8	4
Consumer | Revolving mortgage | 30-59 Days Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans and leases	0	0
Consumer | Revolving mortgage | 60-89 Days Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans and leases	0	0
Consumer | Revolving mortgage | 90 Days or Greater
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans and leases	0	0
SVB
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans and leases	212	174
SVB | Current
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans and leases	206	141
SVB | 30-59 Days Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans and leases	3	2
SVB | 60-89 Days Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans and leases	0	0
SVB | 90 Days or Greater
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans and leases	3	31
SVB | Investor dependent - early stage
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans and leases	25	27
SVB | Investor dependent - early stage | Current
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans and leases	22	22
SVB | Investor dependent - early stage | 30-59 Days Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans and leases	3	2
SVB | Investor dependent - early stage | 60-89 Days Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans and leases	0	0
SVB | Investor dependent - early stage | 90 Days or Greater
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans and leases	0	3
SVB | Investor dependent - growth stage
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans and leases	41	63
SVB | Investor dependent - growth stage | Current
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans and leases	41	63
SVB | Investor dependent - growth stage | 30-59 Days Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans and leases	0	0
SVB | Investor dependent - growth stage | 60-89 Days Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans and leases	0	0
SVB | Investor dependent - growth stage | 90 Days or Greater
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans and leases	0	0
SVB | Innovation C&I and cash flow dependent
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans and leases	146	84
SVB | Innovation C&I and cash flow dependent | Current
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans and leases	143	56
SVB | Innovation C&I and cash flow dependent | 30-59 Days Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans and leases	0	0
SVB | Innovation C&I and cash flow dependent | 60-89 Days Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans and leases	0	0
SVB | Innovation C&I and cash flow dependent | 90 Days or Greater
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans and leases	$ 3	$ 28