Recent Accounting Pronouncements	6 Months Ended
Jun. 30, 2018
Accounting Changes and Error Corrections [Abstract]
Recent Accounting Pronouncements	Recent Accounting Pronouncements On January 1, 2018, Northern Trust adopted ASU No. 2014-09, “Revenue from Contracts with Customers (Topic 606)” (ASU 2014-09). 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. Northern Trust adopted ASU 2014-09 using the modified retrospective method applied to contracts not yet completed as of the date of adoption. Results for reporting periods beginning January 1, 2018 are presented under ASU 2014-09, including certain changes to gross versus net presentation, whereas prior period amounts are not adjusted. The impact of adopting ASU 2014-09 resulted in a $4.0 million reduction in retained earnings. Please refer to Note 14 – “Revenue from Contracts with Clients” for further information. On January 1, 2018, Northern Trust adopted 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 disclosure 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 in the accompanying notes to the financial statements. The impact of adopting ASU 2016-01 resulted in a $0.5 million reduction in retained earnings. On January 1, 2018, Northern Trust adopted ASU No. 2016-15, “Statement of Cash Flows (Topic 230): Classification of Certain Cash Receipts and Cash Payments” (ASU 2016-15). ASU 2016-15 provides guidance on eight specific cash flow issues, thereby reducing diversity in practice in how certain cash receipts and cash payments are presented and classified in the statement of cash flows. Upon adoption of ASU 2016-15, there was no significant impact to Northern Trust’s consolidated statement of cash flows. On January 1, 2018, Northern Trust adopted ASU No. 2016-16, “Income Taxes (Topic 740): Intra-Entity Transfers of Assets Other Than Inventory” (ASU 2016-16). ASU 2016-16 requires an entity to recognize the income tax consequences of intra-entity transfers of assets (excluding inventory) in the period in which the transfer occurs. Upon adoption of ASU 2016-16, there was no significant impact to Northern Trust’s consolidated financial condition or results of operations. On January 1, 2018, Northern Trust adopted ASU No. 2016-18, “Statement of Cash Flows (Topic 230): Restricted Cash (a consensus of the FASB Emerging Issues Task Force)” (ASU 2016-18). ASU 2016-18 requires an entity to include amounts generally described as restricted cash and cash equivalents with cash and cash equivalents when reconciling beginning and end of period total cash balances in the statement of cash flows and as a result, transfers between cash and cash equivalents, and restricted cash and cash equivalents, will not be presented in the statement of cash flows as cash flow activities. Additionally, if the balance sheet includes more than one line item for cash, cash equivalents, restricted cash, and restricted cash and cash equivalents, an entity is required to disclose a reconciliation between the balance sheet and the statement of cash flows. Furthermore, if restricted cash and cash equivalents are material, an entity must disclose information about the nature of restrictions. Upon adoption of ASU 2016-18, there was no significant impact to Northern Trust’s consolidated statement of cash flows. On January 1, 2018, Northern Trust adopted ASU No. 2017-01, “Business Combinations (Topic 805): Clarifying the Definition of a Business” (ASU 2017-01). ASU 2017-01 clarifies the definition of a business with the objective of adding guidance to assist companies with evaluating whether transactions should be accounted for as acquisitions (or disposals) of assets or businesses. The amendments in ASU 2017-01 provide a more robust framework to use in determining when a set of assets and activities is a business. Upon adoption of ASU 2017-01, there was no significant impact to Northern Trust’s consolidated financial condition or results of operations. On January 1, 2018, Northern Trust adopted ASU No. 2017-05, “Other Income-Gains and Losses from the Derecognition of Nonfinancial Assets (Subtopic 610-20): Clarifying the Scope of Asset Derecognition Guidance and Accounting for Partial Sales of Nonfinancial Assets” (ASU 2017-05). ASU 2017-05 clarifies that an in substance nonfinancial asset is an asset or group of assets for which substantially all of the fair value consists of nonfinancial assets and the group or subsidiary is not a business. Transfers of nonfinancial assets to another entity in exchange for a noncontrolling ownership interest in that entity will be accounted for under Accounting Standards Codification 610-20 - Gains and Losses from the Derecognition of Nonfinancial Assets. ASU 2017-05 also impacts the accounting for partial sales of nonfinancial assets, and provides that when an entity transfers its controlling financial interest in a nonfinancial asset, but retains a noncontrolling ownership interest, the entity will measure the retained interest at fair value. This will result in full gain or loss recognition upon the sale of a controlling interest in a nonfinancial asset. Upon adoption of ASU 2017-05, there was no significant impact to Northern Trust’s consolidated financial condition or results of operations. On January 1, 2018, Northern Trust adopted ASU No. 2017-07, “Compensation-Retirement Benefits (Topic 715): Improving the Presentation of Net Periodic Pension Cost and Net Periodic Postretirement Benefit Cost” (ASU 2017-07). Under previous GAAP, net benefit cost on pension and postretirement benefit plans included multiple components, including current-period employee service cost, interest cost on the obligation, expected return on plan assets, and amortization of various amounts deferred from previous periods. ASU 2017-07 requires the bifurcation of the net benefit cost by presenting separately the service cost component from the other components of net benefit cost. Northern Trust provides a detailed breakdown of its net periodic pension costs components including a reference to the respective income statement line in the footnotes and therefore there were no changes to the presentation of net periodic pension costs in the results of operations upon adoption of ASU 2017-07. On January 1, 2018, Northern Trust adopted ASU No. 2017-09, “Compensation - Stock Compensation (Topic 718): Scope of Modification Accounting” (ASU 2017-09). ASU 2017-09 clarifies which types of changes to share-based payment awards are in scope of modification accounting. ASU 2017-09 also provides clarification related to the fair value assessment with respect to determining whether a fair value calculation is required and the appropriate unit of account to apply. Upon adoption of ASU 2017-09, there was no impact to Northern Trust’s consolidated financial condition or results of operations. On January 1, 2018, Northern Trust adopted ASU No. 2018-02, “Income Statement - Reporting Comprehensive Income (Topic 220): Reclassification of Certain Tax Effects from Accumulated Other Comprehensive Income” (ASU 2018-02). The amendments in ASU 2018-02 allow an entity to elect to reclassify from accumulated other comprehensive income to retained earnings the stranded tax effects resulting from the Tax Cuts and Jobs Act. ASU 2018-02 is effective for interim and annual reporting periods beginning after December 15, 2018, however early adoption is permitted. The amendments in ASU 2018-02 may be applied either in the period of adoption or retrospectively to each period (or periods) in which the effect of the change in the U.S. federal corporate income tax rate in the Tax Cuts and Jobs Act is recognized. Upon adoption of ASU 2018-02, Northern Trust elected to reclassify $25.3 million of income tax effects from the Tax Cuts and Jobs Act from accumulated other comprehensive income to retained earnings. In the normal course, it is Northern Trust’s policy to release income tax effects from accumulated other comprehensive income on an aggregate portfolio basis. Please refer to Note 12 – “Accumulated Other Comprehensive Income (Loss)” for further information. On April 1, 2018, Northern Trust adopted ASU No. 2017-12, “Derivatives and Hedging (Topic 815): Targeted Improvements to Accounting for Hedging Activities” (ASU 2017-12). The main provisions of ASU 2017-12 are intended to align better an entity’s risk management activities and financial reporting for hedging relationships through changes to both the designation and measurement guidance for qualifying hedging relationships. ASU 2017-12 eliminates the requirement to measure and report hedge ineffectiveness separately and generally requires the entire change in the fair value of a hedging instrument to be presented in the same income statement line as the hedged item. Further, ASU 2017-12 eases certain documentation and assessment requirements and modifies the accounting for components excluded from the assessment of hedge effectiveness. Northern Trust currently applies the “shortcut” method of accounting available under US GAAP for substantially all fair value hedges and other aspects of Northern Trust’s current hedge accounting program and therefore upon adoption of ASU 2017-12, there was no significant impact to Northern Trust’s consolidated financial condition or results of operations.

Recent Accounting Pronouncements

On January 1, 2018, Northern Trust adopted ASU No. 2014-09, “Revenue from Contracts with Customers (Topic 606)” (ASU 2014-09). 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. Northern Trust adopted ASU 2014-09 using the modified retrospective method applied to contracts not yet completed as of the date of adoption. Results for reporting periods beginning January 1, 2018 are presented under ASU 2014-09, including certain changes to gross versus net presentation, whereas prior period amounts are not adjusted. The impact of adopting ASU 2014-09 resulted in a $4.0 million reduction in retained earnings. Please refer to Note 14 – “Revenue from Contracts with Clients” for further information.

On January 1, 2018, Northern Trust adopted 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 disclosure 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 in the accompanying notes to the financial statements. The impact of adopting ASU 2016-01 resulted in a $0.5 million reduction in retained earnings.

On January 1, 2018, Northern Trust adopted ASU No. 2016-15, “Statement of Cash Flows (Topic 230): Classification of Certain Cash Receipts and Cash Payments” (ASU 2016-15). ASU 2016-15 provides guidance on eight specific cash flow issues, thereby reducing diversity in practice in how certain cash receipts and cash payments are presented and classified in the statement of cash flows. Upon adoption of ASU 2016-15, there was no significant impact to Northern Trust’s consolidated statement of cash flows.

On January 1, 2018, Northern Trust adopted ASU No. 2016-16, “Income Taxes (Topic 740): Intra-Entity Transfers of Assets Other Than Inventory” (ASU 2016-16). ASU 2016-16 requires an entity to recognize the income tax consequences of intra-entity transfers of assets (excluding inventory) in the period in which the transfer occurs. Upon adoption of ASU 2016-16, there was no significant impact to Northern Trust’s consolidated financial condition or results of operations.

On January 1, 2018, Northern Trust adopted ASU No. 2016-18, “Statement of Cash Flows (Topic 230): Restricted Cash (a consensus of the FASB Emerging Issues Task Force)” (ASU 2016-18). ASU 2016-18 requires an entity to include amounts generally described as restricted cash and cash equivalents with cash and cash equivalents when reconciling beginning and end of period total cash balances in the statement of cash flows and as a result, transfers between cash and cash equivalents, and restricted cash and cash equivalents, will not be presented in the statement of cash flows as cash flow activities. Additionally, if the balance sheet includes more than one line item for cash, cash equivalents, restricted cash, and restricted cash and cash equivalents, an entity is required to disclose a reconciliation between the balance sheet and the statement of cash flows. Furthermore, if restricted cash and cash equivalents are material, an entity must disclose information about the nature of restrictions. Upon adoption of ASU 2016-18, there was no significant impact to Northern Trust’s consolidated statement of cash flows.

On January 1, 2018, Northern Trust adopted ASU No. 2017-01, “Business Combinations (Topic 805): Clarifying the Definition of a Business” (ASU 2017-01). ASU 2017-01 clarifies the definition of a business with the objective of adding guidance to assist companies with evaluating whether transactions should be accounted for as acquisitions (or disposals) of assets or businesses. The amendments in ASU 2017-01 provide a more robust framework to use in determining when a set of assets and activities is a business. Upon adoption of ASU 2017-01, there was no significant impact to Northern Trust’s consolidated financial condition or results of operations.

On January 1, 2018, Northern Trust adopted ASU No. 2017-05, “Other Income-Gains and Losses from the Derecognition of Nonfinancial Assets (Subtopic 610-20): Clarifying the Scope of Asset Derecognition Guidance and Accounting for Partial Sales of Nonfinancial Assets” (ASU 2017-05). ASU 2017-05 clarifies that an in substance nonfinancial asset is an asset or group of assets for which substantially all of the fair value consists of nonfinancial assets and the group or subsidiary is not a business. Transfers of nonfinancial assets to another entity in exchange for a noncontrolling ownership interest in that entity will be accounted for under Accounting Standards Codification 610-20 - Gains and Losses from the Derecognition of Nonfinancial Assets. ASU 2017-05 also impacts the accounting for partial sales of nonfinancial assets, and provides that when an entity transfers its controlling financial interest in a nonfinancial asset, but retains a noncontrolling ownership interest, the entity will measure the retained interest at fair value. This will result in full gain or loss recognition upon the sale of a controlling interest in a nonfinancial asset. Upon adoption of ASU 2017-05, there was no significant impact to Northern Trust’s consolidated financial condition or results of operations.

On January 1, 2018, Northern Trust adopted ASU No. 2017-07, “Compensation-Retirement Benefits (Topic 715): Improving the Presentation of Net Periodic Pension Cost and Net Periodic Postretirement Benefit Cost” (ASU 2017-07). Under previous GAAP, net benefit cost on pension and postretirement benefit plans included multiple components, including current-period employee service cost, interest cost on the obligation, expected return on plan assets, and amortization of various amounts deferred from previous periods. ASU 2017-07 requires the bifurcation of the net benefit cost by presenting separately the service cost component from the other components of net benefit cost. Northern Trust provides a detailed breakdown of its net periodic pension costs components including a reference to the respective income statement line in the footnotes and therefore there were no changes to the presentation of net periodic pension costs in the results of operations upon adoption of ASU 2017-07.

On January 1, 2018, Northern Trust adopted ASU No. 2017-09, “Compensation - Stock Compensation (Topic 718): Scope of Modification Accounting” (ASU 2017-09). ASU 2017-09 clarifies which types of changes to share-based payment awards are in scope of modification accounting. ASU 2017-09 also provides clarification related to the fair value assessment with respect to determining whether a fair value calculation is required and the appropriate unit of account to apply. Upon adoption of ASU 2017-09, there was no impact to Northern Trust’s consolidated financial condition or results of operations.

On January 1, 2018, Northern Trust adopted ASU No. 2018-02, “Income Statement - Reporting Comprehensive Income (Topic 220): Reclassification of Certain Tax Effects from Accumulated Other Comprehensive Income” (ASU 2018-02). The amendments in ASU 2018-02 allow an entity to elect to reclassify from accumulated other comprehensive income to retained earnings the stranded tax effects resulting from the Tax Cuts and Jobs Act. ASU 2018-02 is effective for interim and annual reporting periods beginning after December 15, 2018, however early adoption is permitted. The amendments in ASU 2018-02 may be applied either in the period of adoption or retrospectively to each period (or periods) in which the effect of the change in the U.S. federal corporate income tax rate in the Tax Cuts and Jobs Act is recognized. Upon adoption of ASU 2018-02, Northern Trust elected to reclassify $25.3 million of income tax effects from the Tax Cuts and Jobs Act from accumulated other comprehensive income to retained earnings. In the normal course, it is Northern Trust’s policy to release income tax effects from accumulated other comprehensive income on an aggregate portfolio basis. Please refer to Note 12 – “Accumulated Other Comprehensive Income (Loss)” for further information.

On April 1, 2018, Northern Trust adopted ASU No. 2017-12, “Derivatives and Hedging (Topic 815): Targeted Improvements to Accounting for Hedging Activities” (ASU 2017-12). The main provisions of ASU 2017-12 are intended to align better an entity’s risk management activities and financial reporting for hedging relationships through changes to both the designation and measurement guidance for qualifying hedging relationships. ASU 2017-12 eliminates the requirement to measure and report hedge ineffectiveness separately and generally requires the entire change in the fair value of a hedging instrument to be presented in the same income statement line as the hedged item. Further, ASU 2017-12 eases certain documentation and assessment requirements and modifies the accounting for components excluded from the assessment of hedge effectiveness. Northern Trust currently applies the “shortcut” method of accounting available under US GAAP for substantially all fair value hedges and other aspects of Northern Trust’s current hedge accounting program and therefore upon adoption of ASU 2017-12, there was no significant impact to Northern Trust’s consolidated financial condition or results of operations.