Borrowings and Subordinated Debentures - Narrative (Details) - USD ($)	3 Months Ended
Mar. 31, 2024	Dec. 31, 2023
Federal Reserve Bank Advances
Debt Instrument [Line Items]
Balance	$ 0	$ 0
Secured Debt [Member] \| Federal Reserve Bank Advances
Debt Instrument [Line Items]
Borrowing capacity description	6,900,000,000
Collateralized financings	7,700,000,000
Securities loaned, fair value of collateral	1,000,000,000
Secured Debt [Member] \| Bank Term Funding Program \| Federal Reserve Bank Advances
Debt Instrument [Line Items]
Borrowing capacity description	1,500,000,000
Securities loaned, fair value of collateral	1,600,000,000
Unused Lines of Credit
Debt Instrument [Line Items]
Balance	0	0
Current borrowing capacity	290,000,000
Unused commitment fees	0
AFX short-term borrowings
Debt Instrument [Line Items]
Balance	$ 0	$ 0
Credit-Link Notes
Debt Instrument [Line Items]
Variable interest, percentage rate	16.03%	16.02%
Weighted average interest rate	10.70%
Secured debt	$ 2,460,000,000
Other borrowings	$ 123,824,000	$ 123,116,000
Credit-Link Notes \| Highest Rate of Spread
Debt Instrument [Line Items]
Variable interest, percentage rate	13.25%
Credit-Link Notes \| Lowest Rate of Spread
Debt Instrument [Line Items]
Variable interest, percentage rate	8.00%
Federal Home Loan Bank of San Francisco
Debt Instrument [Line Items]
Collateralized financings	$ 10,200,000,000
Securities loaned, fair value of collateral	20,100,000
Letters of credit outstanding, amount	307,400,000	243,800,000
Federal Home Loan Bank of San Francisco \| Secured Debt [Member]
Debt Instrument [Line Items]
Borrowing capacity description	6,300,000,000
Line of credit, current	300,000,000	0
Federal Home Loan Bank of San Francisco \| Secured Debt [Member] \| Bank Term Funding Program
Debt Instrument [Line Items]
Line of credit, current	1,545,000,000	$ 2,618,300,000
Federal Home Loan Bank of San Francisco \| Secured Debt [Member] \| Line Of Credit One
Debt Instrument [Line Items]
Line of credit, current	150,000,000
Federal Home Loan Bank of San Francisco \| Secured Debt [Member] \| Line Of Credit Two
Debt Instrument [Line Items]
Line of credit, current	$ 150,000,000

The value of the collateral (typically cash) that the entity receives in a financing transaction in exchange for securities lent. This item represents a liability in the financial statements of the lender of the securities.

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Amount of commitment fees for the unused borrowing capacity under the long-term financing arrangement that is available to the entity.

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The total amount of the contingent obligation under letters of credit outstanding as of the reporting date.

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No definition available.

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The carrying value as of the balance sheet date of the current and noncurrent portions of long-term obligations drawn from a line of credit, which is a bank's commitment to make loans up to a specific amount. Examples of items that might be included in the application of this element may consist of letters of credit, standby letters of credit, and revolving credit arrangements, under which borrowings can be made up to a maximum amount as of any point in time conditional on satisfaction of specified terms before, as of and after the date of drawdowns on the line. Includes short-term obligations that would normally be classified as current liabilities but for which (a) postbalance sheet date issuance of a long term obligation to refinance the short term obligation on a long term basis, or (b) the enterprise has entered into a financing agreement that clearly permits the enterprise to refinance the short-term obligation on a long term basis and the following conditions are met (1) the agreement does not expire within 1 year and is not cancelable by the lender except for violation of an objectively determinable provision, (2) no violation exists at the BS date, and (3) the lender has entered into the financing agreement is expected to be financially capable of honoring the agreement.

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Amount of current borrowing capacity under the credit facility considering any current restrictions on the amount that could be borrowed (for example, borrowings may be limited by the amount of current assets), but without considering any amounts currently outstanding under the facility.

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Maximum borrowing capacity under the credit facility without consideration of any current restrictions on the amount that could be borrowed or the amounts currently outstanding under the facility.

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The carrying value as of the balance sheet date of the current portion of long-term obligations drawn from a line of credit, which is a bank's commitment to make loans up to a specific amount. Examples of items that might be included in the application of this element may consist of letters of credit, standby letters of credit, and revolving credit arrangements, under which borrowings can be made up to a maximum amount as of any point in time conditional on satisfaction of specified terms before, as of and after the date of drawdowns on the line. Includes short-term obligations that would normally be classified as current liabilities but for which (a) postbalance sheet date issuance of a long term obligation to refinance the short term obligation on a long term basis, or (b) the enterprise has entered into a financing agreement that clearly permits the enterprise to refinance the short-term obligation on a long term basis and the following conditions are met (1) the agreement does not expire within 1 year and is not cancelable by the lender except for violation of an objectively determinable provision, (2) no violation exists at the BS date, and (3) the lender has entered into the financing agreement is expected to be financially capable of honoring the agreement.

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The interest rate applicable to the portion of the carrying amount of long-term borrowings outstanding as of the balance sheet date, including current maturities, which accrues interest at a rate subject to change from time to time.

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The portion of the carrying amount of long-term borrowings outstanding as of the balance sheet date, including current maturities, which accrues interest at a rate subject to change from time to time.

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Weighted average interest rate of long-term debt outstanding calculated at point in time.

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Carrying value as of the balance sheet date, including the current and noncurrent portions, of collateralized debt obligations (with maturities initially due after one year or beyond the operating cycle, if longer). Such obligations include mortgage loans, chattel loans, and any other borrowings secured by assets of the borrower.

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Fair value of the securities pledged as collateral against securities loaned.

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