Contingencies	9 Months Ended
Sep. 30, 2017
Commitments and Contingencies Disclosure [Abstract]
Contingencies	Contingencies Legal and Regulatory Matters In the ordinary course of business, we and our subsidiaries are involved in disputes, litigation, and governmental or regulatory inquiries and investigations, both pending and threatened. These matters, if resolved adversely against us or settled, may result in monetary damages, fines and penalties or require changes in our business practices. The resolution or settlement of these matters is inherently difficult to predict. Based on our assessment of these pending matters, we do not believe that the amount of any judgment, settlement or other action arising from any pending matter is likely to have a material adverse effect on our consolidated financial condition. However, an adverse outcome in certain of the matters described below could have a material adverse effect on our consolidated results of operations for the period in which such matter is resolved, or an accrual is determined to be required, on our consolidated financial condition, or on our reputation. We evaluate our needs for accruals of loss contingencies related to legal and regulatory proceedings on a case-by-case basis. When we have a liability that we deem probable, and we deem the amount of such liability can be reasonably estimated as of the date of our consolidated financial statements, we accrue for our estimate of the amount of loss. We also consider a loss probable and establish an accrual when we make, or intend to make, an offer of settlement. Once established, an accrual is subject to subsequent adjustment as a result of additional information. The resolution of legal and regulatory proceedings and the amount of reasonably estimable loss (or range thereof) are inherently difficult to predict, especially in the early stages of proceedings. Even if a loss is probable, an amount (or range) of loss might not be reasonably estimated until the later stages of the proceeding due to many factors (collectively, "factors influencing reasonable estimates"), such as the presence of complex or novel legal theories, the discretion of governmental authorities in seeking sanctions or negotiating resolutions in civil and criminal matters, the pace and timing of discovery and other assessments of facts and the procedural posture of the matter. As of September 30, 2017, our aggregate accruals for loss contingencies for legal and regulatory matters totaled approximately $15 million. To the extent that we have established accruals in our consolidated statement of condition for probable loss contingencies, such accruals may not be sufficient to cover our ultimate financial exposure associated with any settlements or judgments. Any such ultimate financial exposure, or proceedings to which we may become subject in the future, could have a material adverse effect on our businesses, on our future consolidated financial statements or on our reputation. Except where otherwise noted below, we have not established accruals with respect to the claims discussed and do not believe that potential exposure is probable and can be reasonably estimated. We have identified certain matters for which loss is reasonably possible (but not probable) in future periods, whether in excess of an accrued liability or where there is no accrued liability, and for which we are able to estimate a range of reasonably possible loss. As of September 30, 2017, our estimate of the range of reasonably possible loss for these matters is from zero to approximately $15 million in the aggregate. Our estimate with respect to the aggregate range of reasonably possible loss is based upon currently available information and is subject to significant judgment and a variety of assumptions and known and unknown uncertainties. The matters underlying the estimated range will change from time to time, and actual results may vary significantly from the current estimate. In certain other pending matters , including the Invoicing Matter, Federal Reserve/Massachusetts Division of Banks Written Agreement and Shareholder Litigation discussed below, it is not currently feasible to reasonably estimate the amount or a range of reasonably possible loss (including reasonably possible loss in excess of amounts accrued), and such losses, which may be significant, are not included in the estimate of reasonably possible loss discussed above. This is due to, among other factors, one or more considerations consistent with the factors influencing reasonable estimates described in the above discussion of probable loss accruals. These considerations are particularly prevalent in governmental and regulatory inquiries and investigations and, as a result, reasonably possible loss estimates often are not feasible until the later stages of the inquiry or investigation or of any related legal or regulatory proceeding. An adverse outcome in one or more of the matters for which we do not estimate the amount or a range of reasonably possible loss, individually or in the aggregate, could have a material adverse effect on our businesses, on our future consolidated financial statements or on our reputation. Given that we cannot estimate reasonably possible loss for all legal and regulatory proceedings as to which we may be subject now or in the future, including matters that if adversely concluded may present material financial, regulatory and reputational risks, no conclusion as to the ultimate exposure from current pending or potential legal or regulatory proceedings should be drawn from the current estimate of reasonably possible loss. The following discussion provides information with respect to significant legal, governmental and regulatory matters. Transition Management In January 2014, we entered into a settlement with the FCA, pursuant to which we paid a fine of £22.9 million (approximately $37.8 million), as a result of our having charged six clients of our U.K. transition management business during 2010 and 2011 amounts in excess of the contractual terms. The SEC and the DOJ opened separate investigations into this matter. The U.S. Attorney’s office in Boston has charged three former employees in our transition management business with criminal fraud in connection with their alleged role in this matter. Two of these individuals have pled guilty to one count of criminal conspiracy. Charges remain pending against the third individual. The SEC has also commenced a parallel civil enforcement proceeding against that individual. On January 18, 2017, we announced that we had entered into a settlement agreement with the DOJ and the United States Attorney for the District of Massachusetts to resolve their investigation. Under the terms of the agreement, we, among other things, paid a fine of $32.3 million and entered into a deferred prosecution agreement. Under the deferred prosecution agreement, we agreed to retain an independent compliance and ethics monitor for a term of three years (subject to extension) which will, among other things, review and monitor the effectiveness of our compliance controls and business ethics and make related recommendations. In September 2017, we entered into a settlement with the SEC and paid a penalty of $32.3 million (equal to the fine paid to the DOJ). The SEC settlement also required us to retain an independent ethics and compliance consultant. The monitor appointed in connection with the previously announced DOJ settlement will fulfill that role. Federal Reserve/Massachusetts Division of Banks Written Agreement On June 1, 2015, we entered into a written agreement with the Federal Reserve and the Massachusetts Division of Banks relating to deficiencies identified in our compliance programs with the requirements of the Bank Secrecy Act, AML regulations and U.S. economic sanctions regulations promulgated by OFAC. As part of this enforcement action, we are required to, among other things, implement improvements to our compliance programs and to retain an independent firm to conduct a review of account and transaction activity covering a prior three-month period to evaluate whether any suspicious activity not previously reported should have been identified and reported in accordance with applicable regulatory requirements. To the extent deficiencies in our historical reporting are identified as a result of the transaction review or if we fail to comply with the terms of the written agreement, we may become subject to fines and other regulatory sanctions, which may have a material adverse effect on us. Invoicing Matter In December 2015, we announced a review of the manner in which we invoiced certain expenses to some of our Investment Servicing clients, primarily in the United States, during an 18-year period going back to 1998, and our determination that we had incorrectly invoiced clients for certain expenses. We informed our clients in December 2015 that we will pay to them the amounts we concluded were incorrectly invoiced to them, plus interest. We currently expect the cumulative total of our payments to be at least $340 million (including interest), in connection with that review, which is ongoing. We are implementing enhancements to our billing processes, and we are reviewing the conduct of our employees and have taken appropriate steps to address conduct inconsistent with our standards, including, in some cases, termination of employment. We are also evaluating other billing practices relating to our Investment Servicing clients, including calculation of asset-based fees. We have received a purported class action demand letter alleging that our invoicing practices were unfair and deceptive under Massachusetts law. A class of customers, or particular customers, may assert that we have not paid to them all amounts incorrectly invoiced, and may seek double or treble damages under Massachusetts law. In addition, in March 2017, a purported class action was commenced against us alleging that our invoicing practices violated duties owed to retirement plan customers under ERISA. We are also responding to requests for information from, and are cooperating with investigations by, governmental and regulatory authorities on these matters, including the civil and criminal divisions of the DOJ, the SEC, the DOL, the Massachusetts Attorney General, and the New Hampshire Bureau of Securities Regulation, which could result in significant fines or other sanctions, civil and criminal, against us. If these governmental or regulatory authorities were to conclude that all or a portion of the billing error merited civil or criminal sanctions, any fine or other penalty could be a significant percentage or a multiple of the portion of the overcharging serving as the basis of such a claim or of the full amount of the overcharging. The governmental and regulatory authorities have significant discretion in civil and criminal matters as to the fines and other penalties they seek to impose. The severity of such fines or other penalties could take into account factors such as the amount and duration of our incorrect invoicing, the government’s or regulator's assessment of the conduct of our employees, as well as prior conduct such as that which resulted in our January 2017 deferred prosecution agreement in connection with transition management services and our recent settlement of civil claims regarding our indirect foreign exchange business. Any governmental or regulatory proceeding or sanction or the outcome of any litigation could have a material adverse effect on our reputation or business, including the imposition of restrictions on the operation of our business or a reduction in client demand. Resolution of these matters could also have a material adverse effect on our consolidated results of operations for the period or periods in which such matters are resolved or an accrual is determined to be required. No accrual, other than a reserve for client reimbursement, is reflected on our consolidated statement of condition as of September 30, 2017. Shareholder Litigation A State Street shareholder has filed a purported class action complaint against the Company alleging that the Company’s financial statements in its annual reports for the 2011-14 period were misleading due to the inclusion of revenues associated with the Transition Management and Invoicing matters. In addition, a State Street shareholder has filed a derivative complaint against the Company's past and present officers and directors to recover alleged losses incurred by the Company relating to the Invoicing Matter and to our January 2016 settlement with the SEC concerning Ohio public retirement plans. Income Taxes In determining our provision for income taxes, we make certain judgments and interpretations with respect to tax laws in jurisdictions in which we have business operations. Because of the complex nature of these laws, in the normal course of our business, we are subject to challenges from U.S. and non-U.S. income tax authorities regarding the amount of income taxes due. These challenges may result in adjustments to the timing or amount of taxable income or deductions or the allocation of taxable income among tax jurisdictions. We recognize a tax benefit when it is more likely than not that our position will result in a tax deduction or credit. Unrecognized tax benefits of approximately $63 million as of September 30, 2017 decreased from $71 million as of December 31, 2016. We are presently under audit by a number of tax authorities and the Internal Revenue Service is currently reviewing our U.S. income tax returns for the tax years 2014 and 2015. The earliest tax year open to examination in jurisdictions where we have material operations is 2010. Management believes that we have sufficiently accrued liabilities as of September 30, 2017 for tax exposures.

Legal and Regulatory Matters

In the ordinary course of business, we and our subsidiaries are involved in disputes, litigation, and governmental or regulatory inquiries and investigations, both pending and threatened. These matters, if resolved adversely against us or settled, may result in monetary damages, fines and penalties or require changes in our business practices. The resolution or settlement of these matters is inherently difficult to predict. Based on our assessment of these pending matters, we do not believe that the amount of any judgment, settlement or other action arising from any pending matter is likely to have a material adverse effect on our consolidated financial condition. However, an adverse outcome in certain of the matters described below could have a material adverse effect on our consolidated results of operations for the period in which such matter is resolved, or an accrual is determined to be required, on our consolidated financial condition, or on our reputation.

We evaluate our needs for accruals of loss contingencies related to legal and regulatory proceedings on a case-by-case basis. When we have a liability that we deem probable, and we deem the amount of such liability can be reasonably estimated as of the date of our consolidated financial statements, we accrue for our estimate of the amount of loss. We also consider a loss probable and establish an accrual when we make, or intend to make, an offer of settlement. Once established, an accrual is subject to subsequent adjustment as a result of additional information. The resolution of legal and regulatory proceedings and the amount of reasonably estimable loss (or range thereof) are inherently difficult to predict, especially in the early stages of proceedings. Even if a loss is probable, an amount (or range) of loss might not be reasonably estimated until the later stages of the proceeding due to many factors (collectively, "factors influencing reasonable estimates"), such as the presence of complex or novel legal theories, the discretion of governmental authorities in seeking sanctions or negotiating resolutions in civil and criminal matters, the pace and timing of discovery and other assessments of facts and the procedural posture of the matter.

As of September 30, 2017, our aggregate accruals for loss contingencies for legal and regulatory matters totaled approximately $15 million. To the extent that we have established accruals in our consolidated statement of condition for probable loss contingencies, such accruals may not be sufficient to cover our ultimate financial exposure associated with any settlements or judgments. Any such ultimate financial exposure, or proceedings to which we may become subject in the future, could have a material adverse effect on our businesses, on our future consolidated financial statements or on our reputation. Except where otherwise noted below, we have not established accruals with respect to the claims discussed and do not believe that potential exposure is probable and can be reasonably estimated.

We have identified certain matters for which loss is reasonably possible (but not probable) in future periods, whether in excess of an accrued liability or where there is no accrued liability, and for which we are able to estimate a range of reasonably possible loss. As of September 30, 2017, our estimate of the range of reasonably possible loss for these matters is from zero to approximately $15 million in the aggregate. Our estimate with respect to the aggregate range of reasonably possible loss is based upon currently available information and is subject to significant judgment and a variety of assumptions and known and unknown uncertainties. The matters underlying the estimated range will change from time to time, and actual results may vary significantly from the current estimate.

In certain other pending matters , including the Invoicing Matter, Federal Reserve/Massachusetts Division of Banks Written Agreement and Shareholder Litigation discussed below, it is not currently feasible to reasonably estimate the amount or a range of reasonably possible loss (including reasonably possible loss in excess of amounts accrued), and such losses, which may be significant, are not included in the estimate of reasonably possible loss discussed above. This is due to, among other factors, one or more considerations consistent with the factors influencing reasonable estimates described in the above discussion of probable loss accruals. These considerations are particularly prevalent in governmental and regulatory inquiries and investigations and, as a result, reasonably possible loss estimates often are not feasible until the later stages of the inquiry or investigation or of any related legal or regulatory proceeding. An adverse outcome in one or more of the matters for which we do not estimate the amount or a range of reasonably possible loss, individually or in the aggregate, could have a material adverse effect on our businesses, on our future consolidated financial statements or on our reputation. Given that we cannot estimate reasonably possible loss for all legal and regulatory proceedings as to which we may be subject now or in the future, including matters that if adversely concluded may present material financial, regulatory and reputational risks, no conclusion as to the ultimate exposure from current pending or potential legal or regulatory proceedings should be drawn from the current estimate of reasonably possible loss.

The following discussion provides information with respect to significant legal, governmental and regulatory matters.

Transition Management

In January 2014, we entered into a settlement with the FCA, pursuant to which we paid a fine of £22.9 million (approximately $37.8 million), as a result of our having charged six clients of our U.K. transition management business during 2010 and 2011 amounts in excess of the contractual terms. The SEC and the DOJ opened separate investigations into this matter. The U.S. Attorney’s office in Boston has charged three former employees in our transition management business with criminal fraud in connection with their alleged role in this matter. Two of these individuals have pled guilty to one count of criminal conspiracy. Charges remain pending against the third individual. The SEC has also commenced a parallel civil enforcement proceeding against that individual.

On January 18, 2017, we announced that we had entered into a settlement agreement with the DOJ and the United States Attorney for the District of Massachusetts to resolve their investigation. Under the terms of the agreement, we, among other things, paid a fine of $32.3 million and entered into a deferred prosecution agreement. Under the deferred prosecution agreement, we agreed to retain an independent compliance and ethics monitor for a term of three years (subject to extension) which will, among other things, review and monitor the effectiveness of our compliance controls and business ethics and make related recommendations.

In September 2017, we entered into a settlement with the SEC and paid a penalty of $32.3 million (equal to the fine paid to the DOJ). The SEC settlement also required us to retain an independent ethics and compliance consultant. The monitor appointed in connection with the previously announced DOJ settlement will fulfill that role.

Federal Reserve/Massachusetts Division of Banks Written Agreement

On June 1, 2015, we entered into a written agreement with the Federal Reserve and the Massachusetts Division of Banks relating to deficiencies identified in our compliance programs with the requirements of the Bank Secrecy Act, AML regulations and U.S. economic sanctions regulations promulgated by OFAC. As part of this enforcement action, we are required to, among other things, implement improvements to our compliance programs and to retain an independent firm to conduct a review of account and transaction activity covering a prior three-month period to evaluate whether any suspicious activity not previously reported should have been identified and reported in accordance with applicable regulatory requirements. To the extent deficiencies in our historical reporting are identified as a result of the transaction review or if we fail to comply with the terms of the written agreement, we may become subject to fines and other regulatory sanctions, which may have a material adverse effect on us.

Invoicing Matter

In December 2015, we announced a review of the manner in which we invoiced certain expenses to some of our Investment Servicing clients, primarily in the United States, during an 18-year period going back to 1998, and our determination that we had incorrectly invoiced clients for certain expenses. We informed our clients in December 2015 that we will pay to them the amounts we concluded were incorrectly invoiced to them, plus interest. We currently expect the cumulative total of our payments to be at least $340 million (including interest), in connection with that review, which is ongoing. We are implementing enhancements to our billing processes, and we are reviewing the conduct of our employees and have taken appropriate steps to address conduct inconsistent with our standards, including, in some cases, termination of employment. We are also evaluating other billing practices relating to our Investment Servicing clients, including calculation of asset-based fees.

We have received a purported class action demand letter alleging that our invoicing practices were unfair and deceptive under Massachusetts law. A class of customers, or particular customers, may assert that we have not paid to them all amounts incorrectly invoiced, and may seek double or treble damages under Massachusetts law. In addition, in March 2017, a purported class action was commenced against us alleging that our invoicing practices violated duties owed to retirement plan customers under ERISA.

We are also responding to requests for information from, and are cooperating with investigations by, governmental and regulatory authorities on these matters, including the civil and criminal divisions of the DOJ, the SEC, the DOL, the Massachusetts Attorney General, and the New Hampshire Bureau of Securities Regulation, which could result in significant fines or other sanctions, civil and criminal, against us. If these governmental or regulatory authorities were to conclude that all or a portion of the billing error merited civil or criminal sanctions, any fine or other penalty could be a significant percentage or a multiple of the portion of the overcharging serving as the basis of such a claim or of the full amount of the overcharging. The governmental and regulatory authorities have significant discretion in civil and criminal matters as to the fines and other penalties they seek to impose. The severity of such fines or other penalties could take into account factors such as the amount and duration of our incorrect invoicing, the government’s or regulator's assessment of the conduct of our employees, as well as prior conduct such as that which resulted in our January 2017 deferred prosecution agreement in connection with transition management services and our recent settlement of civil claims regarding our indirect foreign exchange business.

Any governmental or regulatory proceeding or sanction or the outcome of any litigation could have a material adverse effect on our reputation or business, including the imposition of restrictions on the operation of our business or a reduction in client demand. Resolution of these matters could also have a material adverse effect on our consolidated results of operations for the period or periods in which such matters are resolved or an accrual is determined to be required. No accrual, other than a reserve for client reimbursement, is reflected on our consolidated statement of condition as of September 30, 2017.

Shareholder Litigation

A State Street shareholder has filed a purported class action complaint against the Company alleging that the Company’s financial statements in its annual reports for the 2011-14 period were misleading due to the inclusion of revenues associated with the Transition Management and Invoicing matters. In addition, a State Street shareholder has filed a derivative complaint against the Company's past and present officers and directors to recover alleged losses incurred by the Company relating to the Invoicing Matter and to our January 2016 settlement with the SEC concerning Ohio public retirement plans.