Recent Accounting Pronouncements (Policies)	3 Months Ended
Mar. 31, 2016
Accounting Changes and Error Corrections [Abstract]
Recent Accounting Pronouncements	In May 2014, the Financial Accounting Standards Board (FASB) issued Accounting Standards Update (ASU) No. 2014-09, “Revenue from Contracts with Customers (Topic 606)” (ASU 2014-09). ASU 2014-09 is a converged standard between the FASB and the International Accounting Standards Board (IASB) that provides a single comprehensive revenue recognition model for all contracts with customers across transactions and industries. The primary objective of ASU 2014-09 is revenue recognition that represents the transfer of promised goods or services to customers in an amount that reflects the consideration to which the entity expects to be entitled in exchange for those goods or services. ASU 2014-09 is effective for interim and annual reporting periods beginning after December 15, 2017. Northern Trust is currently assessing the impact of adoption of ASU 2014-09. In January 2016, the FASB issued ASU No. 2016-01, “Financial Instruments - Overall (Subtopic 825-10): Recognition and Measurement of Financial Assets and Financial Liabilities” (ASU 2016-01). ASU 2016-01 requires equity investments (except those accounted for under the equity method or those that result in consolidation) to be measured at fair value with changes in fair value recognized in net income unless a policy election is made for investments without readily determinable fair values. Additionally, ASU 2016-01 requires public entities to use the exit price notion when measuring the fair value of financial instruments for measurement purposes and eliminates the requirement to disclose the method(s) and significant assumptions used to estimate the fair value of financial instruments measured at amortized cost on the balance sheet. Furthermore, it requires separate presentation of financial assets and financial liabilities by measurement category and form of financial asset on the balance sheet or the accompanying notes to the financial statements. ASU 2016-01 is effective for interim and annual periods beginning after December 15, 2017. Northern Trust is currently assessing the impact of adoption of ASU 2016-01. In February 2016, the FASB issued ASU No. 2016-02, “Leases (Topic 842)” (ASU 2016-02). ASU 2016-02 introduces a lessee model that brings most leases on the balance sheet, with certain specified scope exceptions. Specifically within the lessee model under ASU 2016-02, a lessee is required to recognize in the statement of financial position a liability to make lease payments, known as the lease liability, and a right-of-use asset representing its right to use the underlying asset over the lease term. While ASU 2016-02 retains a distinction between finance and operating leases similar to current GAAP, it eliminates the required use of bright-line tests for determining the lease classification. ASU 2016-02 is effective for interim and annual reporting periods beginning after December 15, 2018, although early adoption is permitted. Northern Trust is currently assessing the impact of adoption of ASU 2016-02. In March 2016, the FASB issued ASU No. 2016-05, “Derivatives and Hedging (Topic 815): Effect of Derivative Contract Novations on Existing Hedge Accounting Relationships” (ASU 2016-05). ASU 2016-05 clarifies that a change in counterparty to a derivative instrument that has been designated as a hedging instrument under Topic 815 does not, in and of itself, require dedesignation of that hedging relationship provided that all other hedge accounting criteria continue to be met. ASU 2016-05 is effective for interim and annual reporting periods beginning after December 15, 2016, although early adoption is permitted. Although Northern Trust is currently assessing the impact of ASU 2016-05, it is not expected to impact significantly Northern Trust’s consolidated financial position or results of operations. In March 2016, the FASB issued ASU No. 2016-06, “Derivatives and Hedging (Topic 815): Contingent Put and Call Options in Debt Instruments” (ASU 2016-06). The amendments in ASU 2016-06 clarify the steps that are required when assessing whether the economic characteristics and risks of call or put options are clearly and closely related to the economic characteristics and risks of their debt hosts. When a call or put option is contingently exercisable, an entity does not have to assess whether the event that triggers the ability to exercise a call or put option is related to interest rates or credit risks. ASU 2016-06 is effective for interim and annual reporting periods beginning after December 15, 2016, although early adoption is permitted. The adoption of ASU 2016-06 by Northern Trust, effective January 1, 2017, is not expected to impact significantly Northern Trust’s consolidated financial position or results of operations. In March 2016, the FASB issued ASU No. 2016-07, “Investments - Equity Method and Joint Ventures (Topic 323): Simplifying the Transition to the Equity Method of Accounting” (ASU 2016-07). ASU 2016-07 eliminates the requirement to adjust the investment, results of operations, and retained earnings on a retroactive basis when an investment qualifies for use of the equity method as a result of an increase in the level of ownership interest or degree of influence. ASU 2016-07 provides that, upon qualifying for the equity method of accounting, the equity method investor is required to add the cost of acquiring the additional interest in the investee to the current basis of the investor’s previously held interest. ASU 2016-07 is effective for interim and annual reporting periods beginning after December 15, 2016, although early adoption is permitted. Although Northern Trust is currently assessing the impact of ASU 2016-07, it is not expected to impact significantly Northern Trust’s consolidated financial position or results of operations. In March 2016, the FASB issued ASU No. 2016-09, “Compensation - Stock Compensation (Topic 718)” (ASU 2016-09). ASU 2016-09 simplifies several aspects of the accounting for share-based payment transactions, including income tax consequences, classification of awards as either equity or liabilities, and classification on the statement of cash flows. ASU 2016-09 is effective for interim and annual reporting periods beginning after December 15, 2016, although early adoption is permitted. Northern Trust is currently assessing the impact of adoption of ASU 2016-09.

In May 2014, the Financial Accounting Standards Board (FASB) issued Accounting Standards Update (ASU) No. 2014-09, “Revenue from Contracts with Customers (Topic 606)” (ASU 2014-09). ASU 2014-09 is a converged standard between the FASB and the International Accounting Standards Board (IASB) that provides a single comprehensive revenue recognition model for all contracts with customers across transactions and industries. The primary objective of ASU 2014-09 is revenue recognition that represents the transfer of promised goods or services to customers in an amount that reflects the consideration to which the entity expects to be entitled in exchange for those goods or services. ASU 2014-09 is effective for interim and annual reporting periods beginning after December 15, 2017. Northern Trust is currently assessing the impact of adoption of ASU 2014-09.

In January 2016, the FASB issued ASU No. 2016-01, “Financial Instruments - Overall (Subtopic 825-10): Recognition and Measurement of Financial Assets and Financial Liabilities” (ASU 2016-01). ASU 2016-01 requires equity investments (except those accounted for under the equity method or those that result in consolidation) to be measured at fair value with changes in fair value recognized in net income unless a policy election is made for investments without readily determinable fair values. Additionally, ASU 2016-01 requires public entities to use the exit price notion when measuring the fair value of financial instruments for measurement purposes and eliminates the requirement to disclose the method(s) and significant assumptions used to estimate the fair value of financial instruments measured at amortized cost on the balance sheet. Furthermore, it requires separate presentation of financial assets and financial liabilities by measurement category and form of financial asset on the balance sheet or the accompanying notes to the financial statements. ASU 2016-01 is effective for interim and annual periods beginning after December 15, 2017. Northern Trust is currently assessing the impact of adoption of ASU 2016-01.

In February 2016, the FASB issued ASU No. 2016-02, “Leases (Topic 842)” (ASU 2016-02). ASU 2016-02 introduces a lessee model that brings most leases on the balance sheet, with certain specified scope exceptions. Specifically within the lessee model under ASU 2016-02, a lessee is required to recognize in the statement of financial position a liability to make lease payments, known as the lease liability, and a right-of-use asset representing its right to use the underlying asset over the lease term. While ASU 2016-02 retains a distinction between finance and operating leases similar to current GAAP, it eliminates the required use of bright-line tests for determining the lease classification. ASU 2016-02 is effective for interim and annual reporting periods beginning after December 15, 2018, although early adoption is permitted. Northern Trust is currently assessing the impact of adoption of ASU 2016-02.

In March 2016, the FASB issued ASU No. 2016-05, “Derivatives and Hedging (Topic 815): Effect of Derivative Contract Novations on Existing Hedge Accounting Relationships” (ASU 2016-05). ASU 2016-05 clarifies that a change in counterparty to a derivative instrument that has been designated as a hedging instrument under Topic 815 does not, in and of itself, require dedesignation of that hedging relationship provided that all other hedge accounting criteria continue to be met. ASU 2016-05 is effective for interim and annual reporting periods beginning after December 15, 2016, although early adoption is permitted. Although Northern Trust is currently assessing the impact of ASU 2016-05, it is not expected to impact significantly Northern Trust’s consolidated financial position or results of operations.

In March 2016, the FASB issued ASU No. 2016-06, “Derivatives and Hedging (Topic 815): Contingent Put and Call Options in Debt Instruments” (ASU 2016-06). The amendments in ASU 2016-06 clarify the steps that are required when assessing whether the economic characteristics and risks of call or put options are clearly and closely related to the economic characteristics and risks of their debt hosts. When a call or put option is contingently exercisable, an entity does not have to assess whether the event that triggers the ability to exercise a call or put option is related to interest rates or credit risks. ASU 2016-06 is effective for interim and annual reporting periods beginning after December 15, 2016, although early adoption is permitted. The adoption of ASU 2016-06 by Northern Trust, effective January 1, 2017, is not expected to impact significantly Northern Trust’s consolidated financial position or results of operations.

In March 2016, the FASB issued ASU No. 2016-07, “Investments - Equity Method and Joint Ventures (Topic 323): Simplifying the Transition to the Equity Method of Accounting” (ASU 2016-07). ASU 2016-07 eliminates the requirement to adjust the investment, results of operations, and retained earnings on a retroactive basis when an investment qualifies for use of the equity method as a result of an increase in the level of ownership interest or degree of influence. ASU 2016-07 provides that, upon qualifying for the equity method of accounting, the equity method investor is required to add the cost of acquiring the additional interest in the investee to the current basis of the investor’s previously held interest. ASU 2016-07 is effective for interim and annual reporting periods beginning after December 15, 2016, although early adoption is permitted. Although Northern Trust is currently assessing the impact of ASU 2016-07, it is not expected to impact significantly Northern Trust’s consolidated financial position or results of operations.

In March 2016, the FASB issued ASU No. 2016-09, “Compensation - Stock Compensation (Topic 718)” (ASU 2016-09). ASU 2016-09 simplifies several aspects of the accounting for share-based payment transactions, including income tax consequences, classification of awards as either equity or liabilities, and classification on the statement of cash flows. ASU 2016-09 is effective for interim and annual reporting periods beginning after December 15, 2016, although early adoption is permitted. Northern Trust is currently assessing the impact of adoption of ASU 2016-09.