Loans, Allowance for Loan Losses and Allowance for Unfunded Credit Commitments - Composition of Loans, Net of Unearned Income (Additional Information) (Details) - USD ($) $ in Millions	Sep. 30, 2021	Dec. 31, 2020
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, at amortized cost	$ 61,487	$ 45,181
Private bank
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, at amortized cost	8,370	4,901
CRE
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, at amortized cost	2,753	0
Premium wine and other | Premium wine
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, at amortized cost	980	1,053
Premium wine and other | Other
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, at amortized cost	252	28
Real estate secured loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, at amortized cost	11,229	4,940
Real estate secured loans | Private bank
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, at amortized cost	7,400	4,059
Real estate secured loans | Private bank | Loans for personal residence
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, at amortized cost	6,684	3,392
Real estate secured loans | Private bank | Loans to eligible employees
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, at amortized cost	449	481
Real estate secured loans | Private bank | Home equity lines of credit
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, at amortized cost	131	43
Real estate secured loans | Private bank | Other
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, at amortized cost	136	143
Real estate secured loans | CRE
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, at amortized cost	2,753	0
Real estate secured loans | CRE | Multifamily and residential investment
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, at amortized cost	1,047	0
Real estate secured loans | CRE | Retail
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, at amortized cost	564	0
Real estate secured loans | CRE | Office and medical
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, at amortized cost	540	0
Real estate secured loans | CRE | Manufacturing, industrial and warehouse
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, at amortized cost	309	0
Real estate secured loans | CRE | Hospitality
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, at amortized cost	155	0
Real estate secured loans | CRE | Other
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, at amortized cost	138	0
Real estate secured loans | Premium wine and other | Premium wine
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, at amortized cost	795	824
Real estate secured loans | Premium wine and other | Other
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, at amortized cost	$ 281	$ 57