Variable Interest Entities	6 Months Ended
Jun. 30, 2016
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Variable Interest Entities	Variable Interest Entities — Variable Interest Entities (VIEs) are defined within GAAP as entities that either have a total equity investment that is insufficient to permit the entity to finance its activities without additional subordinated financial support or whose equity investors lack the characteristics of a controlling financial interest. Investors that finance a VIE through debt or equity interests, or other counterparties that provide other forms of support, such as guarantees, subordinated fee arrangements, or certain types of derivative contracts, are variable interest holders in the entity. The variable interest holder, if any, that has both the power to direct the activities that most significantly impact the entity and a variable interest that could potentially be significant to the entity is deemed to be the VIE’s primary beneficiary and is required to consolidate the VIE. On January 1, 2016, Northern Trust adopted ASU 2015-02, “Consolidation (Topic 810): Amendments to the Consolidation Analysis” (ASU 2015-02), which modified the Corporation’s evaluation of whether certain legal entities are VIEs, and if Northern Trust would be deemed to be the primary beneficiary of the VIEs. Upon adoption, Northern Trust was not deemed to be the primary beneficiary of the VIEs, and therefore there was no impact to its consolidated financial position or statement of operations. Leveraged Leases. In leveraged leasing transactions, Northern Trust acts as lessor of the underlying asset subject to the lease and typically funds 20 - 30% of the asset’s cost via an equity ownership in a trust with the remaining 70 - 80% provided by third-party non-recourse debt holders. In such transactions, the trusts, which are VIEs, are created to provide the lessee use of the property with substantially all of the rights and obligations of ownership. The lessee’s maintenance and operation of the leased property has a direct effect on the fair value of the underlying property, and the lessee also has the ability to increase the benefits it can receive and limit the losses it can suffer by the manner in which it uses the property. As a result, Northern Trust has determined that it is not the primary beneficiary of these VIEs given it lacks the power to direct the activities that most significantly impact the economic performance of the VIEs. Northern Trust’s maximum exposure to loss as a result of its involvement with the leveraged lease trust VIEs is limited to the carrying amounts of its leveraged lease investments. As of June 30, 2016 and December 31, 2015, the carrying amounts of these investments, which are included in loans and leases in the consolidated balance sheets, were $246.6 million and $389.4 million, respectively. Northern Trust’s funding requirements relative to the VIEs are limited to its invested capital. Northern Trust has no other liquidity arrangements or obligations to purchase assets of the VIEs that would expose Northern Trust to a loss. Tax Credit Structures. Northern Trust invests in qualified affordable housing projects and community development entities (collectively, community development projects) that are designed to generate a return primarily through the realization of tax credits. The community development projects are formed as limited partnerships and LLCs in which Northern Trust invests as a limited partner/investor member through equity contributions. The economic performance of the community development projects, which are VIEs, is subject to the performance of their underlying investment and their ability to operate in compliance with the rules and regulations necessary for the qualification of tax credits generated by equity investments. Northern Trust has determined that it is not the primary beneficiary of any community development projects as it lacks the power to direct the activities that most significantly impact the economic performance of the underlying investments or to affect their ability to operate in compliance with the rules and regulations necessary for the qualification of tax credits generated by equity investments. This power is held by the general partners and managing members who exercise full and exclusive control of the operations of the VIEs. Northern Trust’s maximum exposure to loss as a result of its involvement with community development projects is limited to the carrying amount of its investments, including any undrawn commitments. As of June 30, 2016 and December 31, 2015, the carrying amount of investments in community development projects that generate tax credits, included in other assets in the consolidated balance sheets, totaled $151.1 million and $173.5 million, respectively. As of June 30, 2016 and December 31, 2015, liabilities related to undrawn commitments on investments in tax credit community development projects, included in other liabilities in the consolidated balance sheets, totaled $10.1 million and $10.5 million, respectively. Northern Trust’s funding requirements are limited to its invested capital and undrawn commitments for future equity contributions. Northern Trust has no exposure to loss from liquidity arrangements and no obligation to purchase assets of the community development projects. Affordable housing tax credits and other tax benefits attributable to community development projects totaled $12.0 million and $13.3 million, respectively, for the three months ended June 30, 2016 and 2015, and $24.1 million and $26.5 million, respectively, for the six months ended June 30, 2016 and 2015. Investment Funds. Northern Trust acts as asset manager for various funds in which clients of Northern Trust are investors. As an asset manager of funds, Northern Trust earns a competitively priced fee that is based on assets managed and varies with each fund’s investment objective. Based on its analysis, Northern Trust has determined that it is not the primary beneficiary of these VIEs under GAAP. Some of the funds (Funds) for which Northern Trust acts as asset manager comply or operate in accordance with requirements that are similar to those in Rule 2a-7 of the Investment Company Act of 1940 for registered money market funds and therefore the Funds are exempt from the consolidation requirements in ASU 2015-02. Northern Trust voluntarily waived $0.2 million and $7.9 million of money market mutual fund fees for the three months and six months ended June 30, 2016, respectively. Northern Trust does not have any explicit arrangements to provide financial support to the Funds. Any potential future support of the Funds will be at the discretion of Northern Trust after an evaluation of the specific facts and circumstances. Periodically, Northern Trust makes seed capital investments to certain funds. As of June 30, 2016 Northern Trust had no seed capital investments and no unfunded commitments related to seed capital investments. As of December 31, 2015, Northern Trust had a $25.3 million investment, valued using net asset value per share and included in other assets, and a $25.0 million unfunded commitment related to seed capital investments.

Variable Interest Entities — Variable Interest Entities (VIEs) are defined within GAAP as entities that either have a total equity investment that is insufficient to permit the entity to finance its activities without additional subordinated financial support or whose equity investors lack the characteristics of a controlling financial interest. Investors that finance a VIE through debt or equity interests, or other counterparties that provide other forms of support, such as guarantees, subordinated fee arrangements, or certain types of derivative contracts, are variable interest holders in the entity. The variable interest holder, if any, that has both the power to direct the activities that most significantly impact the entity and a variable interest that could potentially be significant to the entity is deemed to be the VIE’s primary beneficiary and is required to consolidate the VIE.

On January 1, 2016, Northern Trust adopted ASU 2015-02, “Consolidation (Topic 810): Amendments to the Consolidation Analysis” (ASU 2015-02), which modified the Corporation’s evaluation of whether certain legal entities are VIEs, and if Northern Trust would be deemed to be the primary beneficiary of the VIEs. Upon adoption, Northern Trust was not deemed to be the primary beneficiary of the VIEs, and therefore there was no impact to its consolidated financial position or statement of operations.

Leveraged Leases. In leveraged leasing transactions, Northern Trust acts as lessor of the underlying asset subject to the lease and typically funds 20 - 30% of the asset’s cost via an equity ownership in a trust with the remaining 70 - 80% provided by third-party non-recourse debt holders. In such transactions, the trusts, which are VIEs, are created to provide the lessee use of the property with substantially all of the rights and obligations of ownership. The lessee’s maintenance and operation of the leased property has a direct effect on the fair value of the underlying property, and the lessee also has the ability to increase the benefits it can receive and limit the losses it can suffer by the manner in which it uses the property. As a result, Northern Trust has determined that it is not the primary beneficiary of these VIEs given it lacks the power to direct the activities that most significantly impact the economic performance of the VIEs.

Northern Trust’s maximum exposure to loss as a result of its involvement with the leveraged lease trust VIEs is limited to the carrying amounts of its leveraged lease investments. As of June 30, 2016 and December 31, 2015, the carrying amounts of these investments, which are included in loans and leases in the consolidated balance sheets, were $246.6 million and $389.4 million, respectively. Northern Trust’s funding requirements relative to the VIEs are limited to its invested capital. Northern Trust has no other liquidity arrangements or obligations to purchase assets of the VIEs that would expose Northern Trust to a loss.

Tax Credit Structures. Northern Trust invests in qualified affordable housing projects and community development entities (collectively, community development projects) that are designed to generate a return primarily through the realization of tax credits. The community development projects are formed as limited partnerships and LLCs in which Northern Trust invests as a limited partner/investor member through equity contributions. The economic performance of the community development projects, which are VIEs, is subject to the performance of their underlying investment and their ability to operate in compliance with the rules and regulations necessary for the qualification of tax credits generated by equity investments. Northern Trust has determined that it is not the primary beneficiary of any community development projects as it lacks the power to direct the activities that most significantly impact the economic performance of the underlying investments or to affect their ability to operate in compliance with the rules and regulations necessary for the qualification of tax credits generated by equity investments. This power is held by the general partners and managing members who exercise full and exclusive control of the operations of the VIEs.

Northern Trust’s maximum exposure to loss as a result of its involvement with community development projects is limited to the carrying amount of its investments, including any undrawn commitments. As of June 30, 2016 and December 31, 2015, the carrying amount of investments in community development projects that generate tax credits, included in other assets in the consolidated balance sheets, totaled $151.1 million and $173.5 million, respectively. As of June 30, 2016 and December 31, 2015, liabilities related to undrawn commitments on investments in tax credit community development projects, included in other liabilities in the consolidated balance sheets, totaled $10.1 million and $10.5 million, respectively. Northern Trust’s funding requirements are limited to its invested capital and undrawn commitments for future equity contributions. Northern Trust has no exposure to loss from liquidity arrangements and no obligation to purchase assets of the community development projects.

Affordable housing tax credits and other tax benefits attributable to community development projects totaled $12.0 million and $13.3 million, respectively, for the three months ended June 30, 2016 and 2015, and $24.1 million and $26.5 million, respectively, for the six months ended June 30, 2016 and 2015.

Investment Funds. Northern Trust acts as asset manager for various funds in which clients of Northern Trust are investors. As an asset manager of funds, Northern Trust earns a competitively priced fee that is based on assets managed and varies with each fund’s investment objective. Based on its analysis, Northern Trust has determined that it is not the primary beneficiary of these VIEs under GAAP.

Some of the funds (Funds) for which Northern Trust acts as asset manager comply or operate in accordance with requirements that are similar to those in Rule 2a-7 of the Investment Company Act of 1940 for registered money market funds and therefore the Funds are exempt from the consolidation requirements in ASU 2015-02. Northern Trust voluntarily waived $0.2 million and $7.9 million of money market mutual fund fees for the three months and six months ended June 30, 2016, respectively. Northern Trust does not have any explicit arrangements to provide financial support to the Funds. Any potential future support of the Funds will be at the discretion of Northern Trust after an evaluation of the specific facts and circumstances.

Periodically, Northern Trust makes seed capital investments to certain funds. As of June 30, 2016 Northern Trust had no seed capital investments and no unfunded commitments related to seed capital investments. As of December 31, 2015, Northern Trust had a $25.3 million investment, valued using net asset value per share and included in other assets, and a $25.0 million unfunded commitment related to seed capital investments.