Employee Benefits	12 Months Ended
Dec. 31, 2015
Compensation and Retirement Disclosure [Abstract]
Employee Benefits	Employee Benefits Defined Benefit Pension and Other Post-Retirement Benefit Plans: State Street Bank and certain of its U.S. subsidiaries participate in a non-contributory, tax-qualified defined benefit pension plan. The U.S. defined benefit pension plan was frozen as of December 31, 2007 and no new employees were eligible to participate after that date. State Street has agreed to contribute sufficient amounts as necessary to meet the benefits paid to plan participants and to fund the plan’s service cost, plus interest. U.S. employee account balances earn annual interest credits until the employee’s retirement. Non-U.S. employees participate in local defined benefit plans which are funded as required in each local jurisdiction. In addition to the defined benefit pension plans, we have non-qualified unfunded SERPs that provide certain officers with defined pension benefits in excess of allowable qualified plan limits. State Street Bank and certain of its U.S. subsidiaries also participate in a post-retirement plan that provides health care and insurance benefits for certain retired employees. The total expense for these tax-qualified and non-qualified plans was $46 million, $32 million and $42 million for the years ended December 31, 2015, 2014 and 2013, respectively. We recognize the funded status of our defined benefit pension plans and other post-retirement benefit plans, measured as the difference between the fair value of the plan assets and the projected benefit obligation, in the consolidated statement of position. The assets held by the defined benefit pension plans are largely made up of common, collective funds that are liquid and invest principally in U.S. equities and high-quality fixed income investments. The majority of these assets fall within Level 2 of the fair value hierarchy. The benefit obligations associated with our primary U.S. and non-U.S. defined benefit plans, non-qualified unfunded supplemental retirement plans and post-retirement plans were $1.18 billion, $155 million and $30 million, respectively, as of December 31, 2015 and $1.26 billion, $168 million and $120 million, respectively, as of December 31, 2014. As the primary defined benefit plans are frozen, the benefit obligation will only vary over time as a result of changes in market interest rates, the life expectancy of the plan participants and payments made from the plans. The primary U.S. and non-U.S. defined benefit pension plans were underfunded by $16 million and $50 million as of December 31, 2015 and 2014, respectively. The non-qualified supplemental retirement plans were underfunded by $155 million and $168 million as of December 31, 2015 and 2014, respectively. The other post-retirement benefit plans were underfunded by $30 million and $120 million as of December 31, 2015 and 2014, respectively. The underfunded status is included in other liabilities. Defined Contribution Retirement Plans: We contribute to employer-sponsored U.S. and non-U.S. defined contribution plans. Our contribution to these plans was $130 million for 2015, $147 million for 2014 and $134 million for 2013.

Employee Benefits

Defined Benefit Pension and Other Post-Retirement Benefit Plans:

State Street Bank and certain of its U.S. subsidiaries participate in a non-contributory, tax-qualified defined benefit pension plan. The U.S. defined benefit pension plan was frozen as of December 31, 2007 and no new employees were eligible to participate after that date. State Street has agreed to contribute sufficient amounts as necessary to meet the benefits paid to plan participants and to fund the plan’s service cost, plus interest. U.S. employee account balances earn annual interest credits until the employee’s retirement. Non-U.S. employees participate in local defined benefit plans which are funded as required in each local jurisdiction. In addition to the defined benefit pension plans, we have non-qualified unfunded SERPs that provide certain officers with defined pension benefits in excess of allowable qualified plan limits. State Street Bank and certain of its U.S. subsidiaries also participate in a post-retirement plan that provides health care and insurance benefits for certain retired employees. The total expense for these tax-qualified and non-qualified plans was $46 million, $32 million and $42 million for the years ended December 31, 2015, 2014 and 2013, respectively.

We recognize the funded status of our defined benefit pension plans and other post-retirement benefit plans, measured as the difference between the fair value of the plan assets and the projected benefit obligation, in the consolidated statement of position. The assets held by the defined benefit pension plans are largely made up of common, collective funds that are liquid and invest principally in U.S. equities and high-quality fixed income investments. The majority of these assets fall within Level 2 of the fair value hierarchy. The benefit obligations associated with our primary U.S. and non-U.S. defined benefit plans, non-qualified unfunded supplemental retirement plans and post-retirement plans were $1.18 billion, $155 million and $30 million, respectively, as of December 31, 2015 and $1.26 billion, $168 million and $120 million, respectively, as of December 31, 2014. As the primary defined benefit plans are frozen, the benefit obligation will only vary over time as a result of changes in market interest rates, the life expectancy of the plan participants and payments made from the plans. The primary U.S. and non-U.S. defined benefit pension plans were underfunded by $16 million and $50 million as of December 31, 2015 and 2014, respectively. The non-qualified supplemental retirement plans were underfunded by $155 million and $168 million as of December 31, 2015 and 2014, respectively. The other post-retirement benefit plans were underfunded by $30 million and $120 million as of December 31, 2015 and 2014, respectively. The underfunded status is included in other liabilities.

Defined Contribution Retirement Plans:

We contribute to employer-sponsored U.S. and non-U.S. defined contribution plans. Our contribution to these plans was $130 million for 2015, $147 million for 2014 and $134 million for 2013.