Summary of Significant Accounting Policies (Policies)	9 Months Ended
Sep. 30, 2023
Accounting Policies [Abstract]
Basis of Presentation	Basis of Presentation The accounting and financial reporting policies of State Street Corporation conform to U.S. GAAP. State Street Corporation, the Parent Company, is a financial holding company headquartered in Boston, Massachusetts. Unless otherwise indicated or unless the context requires otherwise, all references in these notes to consolidated financial statements to “State Street,” “we,” “us,” “our” or similar references mean State Street Corporation and its subsidiaries on a consolidated basis, including our principal banking subsidiary, State Street Bank.
Consolidation	The consolidated financial statements accompanying these condensed notes are unaudited. In the opinion of management, all adjustments, consisting only of normal recurring adjustments, which are necessary for a fair statement of the consolidated results of operations in these financial statements, have been made. Certain previously reported amounts presented in this Form 10-Q have been reclassified to conform to current-period presentation. Events occurring subsequent to the date of our consolidated statement of condition were evaluated for potential recognition or disclosure in our consolidated financial statements through the date we filed this Form 10-Q with the SEC.
Use of Estimates	The preparation of consolidated financial statements in conformity with U.S. GAAP requires management to make estimates and assumptions in the application of certain of our significant accounting policies that may materially affect the reported amounts of assets, liabilities, equity, revenue and expenses. As a result of unanticipated events or circumstances, actual results could differ from those estimates. These accounting estimates reflect the best judgment of management, but actual results could differ. Our consolidated statement of condition as of December 31, 2022 included in the accompanying consolidated financial statements was derived from the audited financial statements as of that date, but does not include all notes required by U.S. GAAP for a complete set of consolidated financial statements.
Cash and Cash Equivalents	Cash and Cash Equivalents Sanctions programs or government intervention may inhibit our ability to access cash and due from banks in certain accounts. For example, as of September 30, 2023 and December 31, 2022, we held such accounts in Russia, inclusive of $1.4 billion and $767 million, respectively, with our subcustodian, which is an affiliate of a large multinational bank, and with western European-based clearing agencies, for a total of approximately $1.9 billion and $1.3 billion, respectively. Cash and due from banks is evaluated as part of our allowance for credit losses.
Recent Accounting Developments	Recent Accounting Developments In March 2023, the Financial Accounting Standards Board (FASB) issued ASU 2023-02, Investments - Equity Method and Joint Ventures (Topic 323): Accounting for Investments in Tax Credit Structures Using the Proportional Amortization Method, which expands the use of the proportional amortization method to other types of tax credit investments, regardless of the tax credit program from which the income tax credits are received. We adopted the new standard in the second quarter of 2023, effective January 1, 2023, for renewable energy production tax credit investments under the modified retrospective approach. The proportional amortization method better reflects the economics of the investments by amortizing the cost of the investments in proportion to the tax benefits received, and simplifies the presentation of the amortization by recognizing it through Income tax expense. The impact of adoption resulted in a decrease in accrued expenses and other liabilities, a decrease in other assets and was not material to retained earnings. Additionally, we continue to evaluate other accounting standards that were recently issued, but not yet adopted as of September 30, 2023; none are expected to have a material impact to our financial statements.
Fair Value Measurements	Fair Value Measurements We carry trading account assets and liabilities, AFS debt securities, certain equity securities and various types of derivative financial instruments, at fair value in our consolidated statement of condition on a recurring basis. Changes in the fair values of these financial assets and liabilities are recorded either as components of our consolidated statement of income or as components of AOCI within shareholders' equity in our consolidated statement of condition. We measure fair value for the above-described financial assets and liabilities in conformity with U.S. GAAP that governs the measurement of the fair value of financial instruments. Management believes that its valuation techniques and underlying assumptions used to measure fair value conform to the provisions of U.S. GAAP. We categorize the financial assets and liabilities that we carry at fair value based on a prescribed three-level valuation hierarchy. For information about our valuation techniques for financial assets and financial liabilities measured at fair value and the fair value hierarchy, refer to pages 133 to 139 in Note 2 to the consolidated financial statements included under Item 8, Financial Statements and Supplementary Data, in our 2022 Form 10-K.

Summary of Significant Accounting Policies (Policies)

9 Months Ended

Sep. 30, 2023

The accounting and financial reporting policies of State Street Corporation conform to U.S. GAAP. State Street Corporation, the Parent Company, is a financial holding company headquartered in Boston, Massachusetts. Unless otherwise indicated or unless the context requires otherwise, all references in these notes to consolidated financial statements to “State Street,” “we,” “us,” “our” or similar references mean State Street Corporation and its subsidiaries on a consolidated basis, including our principal banking subsidiary, State Street Bank.

Consolidation

The consolidated financial statements accompanying these condensed notes are unaudited. In the opinion of management, all adjustments, consisting only of normal recurring adjustments, which are necessary for a fair statement of the consolidated results of operations in these financial statements, have been made. Certain previously reported amounts presented in this Form 10-Q have been reclassified to conform to current-period presentation. Events occurring subsequent to the date of our consolidated statement of condition were evaluated for potential recognition or disclosure in our consolidated financial statements through the date we filed this Form 10-Q with the SEC.

Use of Estimates

The preparation of consolidated financial statements in conformity with U.S. GAAP requires management to make estimates and assumptions in the application of certain of our significant accounting policies that may materially affect the reported amounts of assets, liabilities, equity, revenue and expenses. As a result of unanticipated events or circumstances, actual results could differ from those estimates. These accounting estimates reflect the best judgment of management, but actual results could differ.

Our consolidated statement of condition as of December 31, 2022 included in the accompanying consolidated financial statements was derived from the audited financial statements as of that date, but does not include all notes required by U.S. GAAP for a complete set of consolidated financial statements.

Cash and Cash Equivalents

Sanctions programs or government intervention may inhibit our ability to access cash and due from banks in certain accounts. For example, as of September 30, 2023 and December 31, 2022, we held such accounts in Russia, inclusive of $1.4 billion and $767 million, respectively, with our subcustodian, which is an affiliate of a large multinational bank, and with western European-based clearing agencies, for a total of approximately $1.9 billion and $1.3 billion, respectively. Cash and due from banks is evaluated as part of our allowance for credit losses.

Recent Accounting Developments

In March 2023, the Financial Accounting Standards Board (FASB) issued ASU 2023-02, Investments - Equity Method and Joint Ventures (Topic 323): Accounting for Investments in Tax Credit Structures Using the Proportional Amortization Method, which expands the use of the proportional amortization method to other types of tax credit investments, regardless of the tax credit program from which the income tax credits are received. We adopted the new standard in the second quarter of 2023, effective January 1, 2023, for renewable energy production tax credit investments under the modified retrospective approach. The proportional amortization method better reflects the economics of the investments by amortizing the cost of the investments in proportion to the tax benefits received, and simplifies the presentation of the amortization by recognizing it through Income tax expense. The impact of adoption resulted in a decrease in accrued expenses and other liabilities, a decrease in other assets and was not material to retained earnings.

Additionally, we continue to evaluate other accounting standards that were recently issued, but not yet adopted as of September 30, 2023; none are expected to have a material impact to our financial statements.

Fair Value Measurements

We carry trading account assets and liabilities, AFS debt securities, certain equity securities and various types of derivative financial instruments, at fair value in our consolidated statement of condition on a recurring basis. Changes in the fair values of these financial assets and liabilities are recorded either as components of our consolidated statement of income or as components of AOCI within shareholders' equity in our consolidated statement of condition.

We measure fair value for the above-described financial assets and liabilities in conformity with U.S. GAAP that governs the measurement of the fair value of financial instruments. Management believes that its valuation techniques and underlying assumptions used to measure fair value conform to the provisions of U.S. GAAP. We categorize the financial assets and liabilities that we carry at fair value based on a prescribed three-level valuation

hierarchy. For information about our valuation techniques for financial assets and financial liabilities measured at fair value and the fair value hierarchy, refer to pages 133 to 139 in Note 2 to the consolidated financial statements included under Item 8, Financial Statements and Supplementary Data, in our 2022 Form 10-K.