Summary of Significant Accounting Policies	6 Months Ended
Jun. 30, 2015
Accounting Policies [Abstract]
Summary of Significant Accounting Policies	Summary of Significant Accounting Policies The accounting and financial reporting policies of State Street Corporation conform to U.S. generally accepted accounting principles, referred to as 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. Our principal banking subsidiary is State Street Bank and Trust Company, or State Street Bank. The accompanying Consolidated Financial Statements should be read in conjunction with the financial and risk factor information included in our 2014 Annual Report on Form 10-K (2014 Form 10-K), which we previously filed with the Securities and Exchange Commission, or SEC. 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. The preparation of consolidated financial statements in conformity with 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, 2014 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 GAAP for a complete set of consolidated financial statements. Recent Accounting Developments: In July 2015, the Financial Accounting Standards Board, or the FASB, decided to delay the effective date of the new revenue standard by one year. The deferral results in the new revenue standard being effective for State Street beginning on January 1, 2018. In May 2015, the FASB published an amendment, which makes certain technical corrections to the FASB Accounting Standards Codification that affect a wide variety of topics to clarify the codification, correct unintended application of the guidance, or make minor improvements that are not expected to have a significant effect on current accounting practice or create a significant administrative cost to entities. The amendments that require transition guidance are effective for State Street beginning on January 1, 2016 and all other amendments are effective immediately. Our adoption of this amendment does not have a material impact on our consolidated financial statements. In May 2015, the FASB issued an amendment to GAAP which removes from the fair value hierarchy, investments for which the practical expedient is used to measure fair value at net asset value (NAV). Instead, an entity is required to include those investments as a reconciling line item so that the total fair value amount of investments in the disclosure is consistent with the amount on the balance sheet. The amendment is effective for State Street beginning on January 1, 2016. Our adoption of this amendment is not expected to have a material effect on our consolidated financial statements In April 2015, the FASB issued an amendment to GAAP which will assist entities in evaluating the accounting for fees paid by a customer in a cloud computing arrangement. The amendment, which allows for early adoption, is effective for State Street beginning on January 1, 2016. Our adoption of this amendment is not expected to have a material effect on our consolidated financial statements. In April 2015, the FASB issued an amendment to GAAP that requires debt issuance costs to be presented in the consolidated balance sheet as a direct deduction from the carrying value of the associated debt liability, consistent with the presentation of a debt discount. The amendment, which allows for early adoption, is effective for State Street beginning on January 1, 2016. Our debt issuance costs that are currently classified as deferred credits and have a balance of approximately $27 million as of June 30, 2015 will be reclassified as contra liabilities upon adoption. In February 2015, the FASB issued an amendment to GAAP that updates the consolidation model used to evaluate whether a legal entity is required to be consolidated. The amendment, which allows for early adoption, is effective for State Street beginning on January 1, 2016, and may be applied retrospectively or via a modified retrospective approach. Although we are currently assessing the potential impact of this amendment on our consolidated financial statements, we do not expect our adoption of this amendment to have a material effect on our consolidated financial statements. In February 2015, the FASB issued an amendment to GAAP to remove the concept of "extraordinary items," which are defined as items that are unusual and infrequent in nature. The amendment, which allows for early adoption, is effective for State Street beginning on January 1, 2016. Our adoption of this amendment is not expected to have a material effect on our consolidated financial statements.

Summary of Significant Accounting Policies

The accounting and financial reporting policies of State Street Corporation conform to U.S. generally accepted accounting principles, referred to as 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. Our principal banking subsidiary is State Street Bank and Trust Company, or State Street Bank.

The accompanying Consolidated Financial Statements should be read in conjunction with the financial and risk factor information included in our 2014 Annual Report on Form 10-K (2014 Form 10-K), which we previously filed with the Securities and Exchange Commission, or SEC.

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.

The preparation of consolidated financial statements in conformity with 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, 2014 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 GAAP for a complete set of consolidated financial statements.

Recent Accounting Developments:

In July 2015, the Financial Accounting Standards Board, or the FASB, decided to delay the effective date of the new revenue standard by one year. The deferral results in the new revenue standard being effective for State Street beginning on January 1, 2018.

In May 2015, the FASB published an amendment, which makes certain technical corrections to the FASB Accounting Standards Codification that affect a wide variety of topics to clarify the codification, correct unintended application of the guidance, or make minor improvements that are not expected to have a significant effect on current accounting practice or create a significant administrative cost to entities. The amendments that require transition guidance are effective for State Street beginning on January 1, 2016 and all other amendments are effective immediately. Our adoption of this amendment does not have a material impact on our consolidated financial statements.

In May 2015, the FASB issued an amendment to GAAP which removes from the fair value hierarchy, investments for which the practical expedient is used to measure fair value at net asset value (NAV). Instead, an entity is required to include those investments as a reconciling line item so that the total fair value amount of investments in the disclosure is consistent with the amount on the balance sheet. The amendment is effective for State Street beginning on January 1, 2016. Our adoption of this amendment is not expected to have a material effect on our consolidated financial statements

In April 2015, the FASB issued an amendment to GAAP which will assist entities in evaluating the accounting for fees paid by a customer in a cloud computing arrangement. The amendment, which allows for early adoption, is effective for State Street beginning on January 1, 2016. Our adoption of this amendment is not expected to have a material effect on our consolidated financial statements.

In April 2015, the FASB issued an amendment to GAAP that requires debt issuance costs to be presented in the consolidated balance sheet as a direct deduction from the carrying value of the associated debt liability, consistent with the presentation of a debt discount. The amendment, which allows for early adoption, is effective for State Street beginning on January 1, 2016.

Our debt issuance costs that are currently classified as deferred credits and have a balance of approximately $27 million as of June 30, 2015 will be reclassified as contra liabilities upon adoption.

In February 2015, the FASB issued an amendment to GAAP that updates the consolidation model used to evaluate whether a legal entity is required to be consolidated. The amendment, which allows for early adoption, is effective for State Street beginning on January 1, 2016, and may be applied retrospectively or via a modified retrospective approach. Although we are currently assessing the potential impact of this amendment on our consolidated financial statements, we do not expect our adoption of this amendment to have a material effect on our consolidated financial statements.

In February 2015, the FASB issued an amendment to GAAP to remove the concept of "extraordinary items," which are defined as items that are unusual and infrequent in nature. The amendment, which allows for early adoption, is effective for State Street beginning on January 1, 2016. Our adoption of this amendment is not expected to have a material effect on our consolidated financial statements.