Variable Interest Entities	12 Months Ended
Dec. 31, 2015
Variable Interest Entities [Abstract]
Variable Interest Entities	Variable Interest Entities We are involved, in the normal course of our business, with various types of special purpose entities, some of which meet the definition of VIEs. We are required by U.S. GAAP to consolidate a VIE when we are deemed to be the primary beneficiary. This determination is evaluated periodically as facts and circumstances change. Asset-Backed Investment Securities: We invest in various forms of asset-backed securities, which we carry in our investment securities portfolio. These asset-backed securities meet the U.S. GAAP definition of asset securitization entities, which are considered to be VIEs. We are not considered to be the primary beneficiary of these VIEs since we do not have control over their activities. Additional information about our asset-backed securities is provided in Note 3. Tax-Exempt Investment Program: In the normal course of our business, we structure and sell certificated interests in pools of tax-exempt investment-grade assets, principally to our mutual fund clients. We structure these pools as partnership trusts, and the assets and liabilities of the trusts are recorded in our consolidated statement of condition as AFS investment securities and other short-term borrowings. As of December 31, 2015 and 2014, we carried AFS investment securities, composed of securities related to state and political subdivisions, with a fair value of $2.10 billion and $2.27 billion, respectively, and other short-term borrowings of $1.75 billion and $1.87 billion, respectively, in our consolidated statement of condition in connection with these trusts. The interest revenue and interest expense generated by the investments and certificated interests, respectively, are recorded as components of net interest revenue when earned or incurred. We transfer assets to the trusts from our investment securities portfolio at adjusted book value, and the trusts finance the acquisition of these assets by selling certificated interests issued by the trusts to third-party investors and to State Street as residual holder. These transfers do not meet the de-recognition criteria defined by U.S. GAAP, and therefore, the assets continue to be recorded in our consolidated financial statements. The trusts had a weighted-average life of approximately 5.4 years as of December 31, 2015, compared to approximately 5.9 years as of December 31, 2014. Under separate legal agreements, we provide standby bond-purchase agreements to these trusts and, with respect to certain securities, letters of credit. Our commitments to the trusts under these standby bond-purchase agreements and letters of credit totaled $1.75 billion and $569 million, respectively, as of December 31, 2015, none of which was utilized as of that date. In the event that our obligations under these agreements are triggered, no material impact to our consolidated results of operations or financial condition is expected to occur, because the securities are already recorded at fair value in our consolidated statement of condition. In addition, neither creditors nor third-party investors in the trusts have any recourse to State Street’s general credit. Interests in Sponsored Investment Funds: In the normal course of business, we manage various types of sponsored investment funds through SSGA. The services we provide to these sponsored investment funds generate management fee revenue. From time to time, we may invest cash in the funds, which we refer to as seed capital, in order for the funds to establish a performance history for newly-launched strategies. With respect to our interests in sponsored investment funds that meet the definition of a VIE, a primary beneficiary assessment is performed to determine if our variable interest (or combination of variable interests, including those of related parties) absorbs the majority of the entity’s expected losses, receives a majority of the entity’s expected residual returns, or both. As part of our assessment, we consider all the facts and circumstances regarding the terms and characteristics of the variable interest(s), the design and characteristics of the fund and the other involvements of the enterprise with the fund. Upon consolidation of certain sponsored investment funds, we retain the specialized investment company accounting rules followed by the underlying funds. All of the underlying investments held by such consolidated sponsored investment funds are carried at fair value, with corresponding changes in the investments’ fair values reflected in trading services revenue in our consolidated statement of income. When we no longer control these funds due to a reduced ownership interest or other reasons, the funds are de-consolidated and accounted for under another accounting method if we continue to maintain an investment in the fund. As of December 31, 2015, the aggregate assets and liabilities of our consolidated sponsored investment funds totaled $321 million and $228 million, respectively. As of December 31, 2014, the aggregate assets and liabilities of our consolidated sponsored investment funds totaled $65 million and $13 million, respectively. As of December 31, 2015, our potential maximum total exposure associated with the consolidated sponsored investment funds totaled $61 million and represented the value of our economic ownership interest in the fund. We expect any financial losses that we realize over time from these seed investments to be limited to the actual fair value of the amount invested in the consolidated fund, which is based on the fair value of the underlying investment securities held by the funds. However, in the event of a fund wind-down, gross gains and losses of the fund may be recognized for financial accounting purposes in different periods during the time the fund is consolidated but not wholly owned. Although we expect the actual economic loss to be limited to the amount invested, our losses in any period could exceed the value of our economic interests in the fund and could exceed the value of our initial seed capital investment. Our conclusion to consolidate a sponsored investment fund may vary from period to period, most commonly as a result of fluctuation in our ownership interest as a result of changes in the number of fund shares held by either us or by third parties. Given that the funds follow specialized investment company accounting rules which prescribe fair value, a de-consolidation generally would not result in gains or losses for us. The net assets of any consolidated fund are solely available to settle the liabilities of the fund and to settle any investors’ ownership redemption requests, including any seed capital invested in the fund by State Street. We are not contractually required to provide financial or any other support to any of our sponsored investment funds. In addition, neither creditors nor equity investors in the sponsored investment funds have any recourse to State Street’s general credit. As of December 31, 2015 and 2014, we managed certain sponsored investment funds, considered VIEs, in which we held a variable interest but for which we were not deemed to be the primary beneficiary. Our potential maximum loss exposure related to these unconsolidated funds totaled $75 million and $45 million as of December 31, 2015 and 2014, respectively, and represented the carrying value of our seed capital investment, which is recorded in either AFS investment securities or other assets in our consolidated statement of condition. The amount of loss we may recognize during any period is limited to the carrying amount of our seed capital investment in the unconsolidated fund.

Variable Interest Entities

We are involved, in the normal course of our business, with various types of special purpose entities, some of which meet the definition of VIEs. We are required by U.S. GAAP to consolidate a VIE when we are deemed to be the primary beneficiary. This determination is evaluated periodically as facts and circumstances change.

Asset-Backed Investment Securities:

We invest in various forms of asset-backed securities, which we carry in our investment securities portfolio. These asset-backed securities meet the U.S. GAAP definition of asset securitization entities, which are considered to be VIEs. We are not considered to be the primary beneficiary of these VIEs since we do not have control over their activities. Additional information about our asset-backed securities is provided in Note 3.

Tax-Exempt Investment Program:

In the normal course of our business, we structure and sell certificated interests in pools of tax-exempt investment-grade assets, principally to our mutual fund clients. We structure these pools as partnership trusts, and the assets and liabilities of the trusts are recorded in our consolidated statement of condition as AFS investment securities and other short-term borrowings. As of December 31, 2015 and 2014, we carried AFS investment securities, composed of securities related to state and political subdivisions, with a fair value of $2.10 billion and $2.27 billion, respectively, and other short-term borrowings of $1.75 billion and $1.87 billion, respectively, in our consolidated statement of condition in connection with these trusts. The interest revenue and interest expense generated by the investments and certificated interests, respectively, are recorded as components of net interest revenue when earned or incurred.

We transfer assets to the trusts from our investment securities portfolio at adjusted book value, and the trusts finance the acquisition of these assets by selling certificated interests issued by the trusts to third-party investors and to State Street as residual holder. These transfers do not meet the de-recognition criteria defined by U.S. GAAP, and therefore, the assets continue to be recorded in our consolidated financial statements. The trusts had a weighted-average life of approximately 5.4 years as of December 31, 2015, compared to approximately 5.9 years as of December 31, 2014.

Under separate legal agreements, we provide standby bond-purchase agreements to these trusts and, with respect to certain securities, letters of credit. Our commitments to the trusts under these standby bond-purchase agreements and letters of credit totaled $1.75 billion and $569 million, respectively, as of December 31, 2015, none of which was utilized as of that date. In the event that our obligations under these agreements are triggered, no material impact to our consolidated results of operations or financial condition is expected to occur, because the securities are already recorded at fair value in our consolidated statement of condition. In addition, neither creditors nor third-party investors in the trusts have any recourse to State Street’s general credit.

Interests in Sponsored Investment Funds:

In the normal course of business, we manage various types of sponsored investment funds through SSGA. The services we provide to these sponsored investment funds generate management fee revenue. From time to time, we may invest cash in the funds, which we refer to as seed capital, in order for the funds to establish a performance history for newly-launched strategies.

With respect to our interests in sponsored investment funds that meet the definition of a VIE, a primary beneficiary assessment is performed to determine if our variable interest (or combination of variable interests, including those of related parties) absorbs the majority of the entity’s expected losses, receives a majority of the entity’s expected residual returns, or both. As part of our assessment, we consider all the facts and circumstances regarding the terms and characteristics of the variable interest(s), the design and characteristics of the fund and the other involvements of the enterprise with the fund. Upon consolidation of certain sponsored investment funds, we retain the specialized investment company accounting rules followed by the underlying funds.

All of the underlying investments held by such consolidated sponsored investment funds are carried at fair value, with corresponding changes in the investments’ fair values reflected in trading services revenue in our consolidated statement of income. When we no longer control these funds due to a reduced ownership interest or other reasons, the funds are de-consolidated and accounted for under another accounting method if we continue to maintain an investment in the fund.

As of December 31, 2015, the aggregate assets and liabilities of our consolidated sponsored investment funds totaled $321 million and $228 million, respectively. As of December 31, 2014, the aggregate assets and liabilities of our consolidated sponsored investment funds totaled $65 million and $13 million, respectively.

As of December 31, 2015, our potential maximum total exposure associated with the consolidated sponsored investment funds totaled $61 million and represented the value of our economic ownership interest in the fund. We expect any financial losses that we realize over time from these seed investments to be limited to the actual fair value of the amount invested in the consolidated fund, which is based on the fair value of the underlying investment securities held by the funds. However, in the event of a fund wind-down, gross gains and losses of the fund may be recognized for financial accounting purposes in different periods during the time the fund is consolidated but not wholly owned. Although we expect the actual economic loss to be limited to the amount invested, our losses in any period could exceed the value of our economic interests in the fund and could exceed the value of our initial seed capital investment.

Our conclusion to consolidate a sponsored investment fund may vary from period to period, most commonly as a result of fluctuation in our ownership interest as a result of changes in the number of fund shares held by either us or by third parties. Given that the funds follow specialized investment company accounting rules which prescribe fair value, a de-consolidation generally would not result in gains or losses for us.

The net assets of any consolidated fund are solely available to settle the liabilities of the fund and to settle any investors’ ownership redemption requests, including any seed capital invested in the fund by State Street. We are not contractually required to provide financial or any other support to any of our sponsored investment funds. In addition, neither creditors nor equity investors in the sponsored investment funds have any recourse to State Street’s general credit.

As of December 31, 2015 and 2014, we managed certain sponsored investment funds, considered VIEs, in which we held a variable interest but for which we were not deemed to be the primary beneficiary. Our potential maximum loss exposure related to these unconsolidated funds totaled $75 million and $45 million as of December 31, 2015 and 2014, respectively, and represented the carrying value of our seed capital investment, which is recorded in either AFS investment securities or other assets in our consolidated statement of condition. The amount of loss we may recognize during any period is limited to the carrying amount of our seed capital investment in the unconsolidated fund.