Recent Accounting Pronouncements	12 Months Ended
Dec. 31, 2016
Accounting Changes and Error Corrections [Abstract]
Recent Accounting Pronouncements	Recent Accounting Pronouncements On January 1, 2016, the Corporation 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 Variable Interest Entities (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. In March 2016, the Financial Accounting Standards Board (FASB) issued ASU No. 2016-09, “Compensation - Stock Compensation (Topic 718): Improvements to Employee Share-Based Payment Accounting.” ASU No. 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. The Corporation early adopted ASU No. 2016-09 with an effective date of January 1, 2016. As a result of the adoption, during the year ended December 31, 2016, the Corporation recognized a benefit of $12.3 million in provision for income taxes for excess tax benefits associated with share-based payment transactions. For all years prior to the year ended December 31, 2016, these excess tax benefits were recognized in additional paid-in capital. For the year ended December 31, 2016, the Corporation reclassified excess tax benefits from other financing activities to other operating activities and for the years ended December, 31 2016, 2015 and 2014, the Corporation classified taxes paid related to net share settlement of equity awards in financing activities in the consolidated statements of cash flows, respectively. The Corporation had no previously unrecognized excess tax benefits; therefore, there was no impact to the consolidated financial statements as it related to the elimination of the requirement that excess tax benefits be realized before recognition. The Corporation elected to retain its existing accounting policy regarding award forfeitures.

Recent Accounting Pronouncements

On January 1, 2016, the Corporation 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 Variable Interest Entities (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.

In March 2016, the Financial Accounting Standards Board (FASB) issued ASU No. 2016-09, “Compensation - Stock Compensation (Topic 718): Improvements to Employee Share-Based Payment Accounting.” ASU No. 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.

The Corporation early adopted ASU No. 2016-09 with an effective date of January 1, 2016. As a result of the adoption, during the year ended December 31, 2016, the Corporation recognized a benefit of $12.3 million in provision for income taxes for excess tax benefits associated with share-based payment transactions. For all years prior to the year ended December 31, 2016, these excess tax benefits were recognized in additional paid-in capital.

For the year ended December 31, 2016, the Corporation reclassified excess tax benefits from other financing activities to other operating activities and for the years ended December, 31 2016, 2015 and 2014, the Corporation classified taxes paid related to net share settlement of equity awards in financing activities in the consolidated statements of cash flows, respectively.

The Corporation had no previously unrecognized excess tax benefits; therefore, there was no impact to the consolidated financial statements as it related to the elimination of the requirement that excess tax benefits be realized before recognition.

The Corporation elected to retain its existing accounting policy regarding award forfeitures.