Significant Accounting Policies	3 Months Ended
Mar. 31, 2019
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Significant Accounting Policies	Significant Accounting Policies Financial Statements— The unaudited financial statements included herein have been prepared by Illinois Tool Works Inc. and Subsidiaries (the “Company”). In the opinion of management, the interim financial statements reflect all adjustments of a normal recurring nature necessary for a fair statement of the results for interim periods. It is suggested that these financial statements be read in conjunction with the financial statements and notes to financial statements included in the Company’s 2018 Annual Report on Form 10-K. Certain reclassifications of prior year data have been made to conform with current year reporting. New Accounting Pronouncements In May 2014, the Financial Accounting Standards Board (the "FASB") issued authoritative guidance to change the criteria for revenue recognition. The core principle of the new guidance is that revenue should be recognized to depict the transfer of control 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. In addition, expanded revenue disclosures are required. The Company's sales arrangements with customers are predominantly short-term in nature and generally provide for transfer of control and risks and rewards of ownership at the time of product shipment or delivery of service. As such, the timing of revenue recognition under both the prior and new guidance is the same for the majority of the Company’s transactions. Effective January 1, 2018, the Company adopted the new revenue recognition guidance under the modified retrospective method and recorded a cumulative-effect adjustment reducing retained earnings by $9 million as of January 1, 2018. In February 2016, the FASB issued authoritative guidance to change the criteria for recognizing leasing transactions. The primary change under the new guidance is that a lessee is required to recognize a lease liability and corresponding right-of-use asset for its operating leases. The new guidance also requires additional disclosures. Effective January 1, 2019, the Company adopted the new guidance prospectively for all operating lease transactions as of and after the effective date with a noncancellable lease term greater than one year. Upon adoption, the Company recorded a lease liability of $205 million and a corresponding right-of-use asset. The new guidance did not have a material impact on the results of operations or cash flows for the three months ended March 31, 2019. Refer to Note 5. Leases for additional information regarding the Company’s lease transactions. In October 2016, the FASB issued authoritative guidance requiring the recognition of the income tax consequences of an intra-entity transfer of an asset, other than inventory, when the transfer occurs rather than when transferred to a third party as required under the prior guidance. The provisions of the new guidance are being applied prospectively to intra-entity asset transfers on or after January 1, 2018 and may result in future tax rate volatility. Upon adoption of the new guidance on January 1, 2018, the Company recorded a cumulative-effect adjustment reducing deferred tax assets and retained earnings by $406 million. In August 2017, the FASB issued authoritative guidance which includes targeted improvements to simplify the application of hedge accounting and improve financial reporting of hedging activities. Effective January 1, 2019, the Company adopted the new guidance which did not have a material impact on the results of operations, financial position or cash flows. In February 2018, the FASB issued authoritative guidance which allows for an optional one-time reclassification of the stranded tax effects resulting from the change in the U.S. federal corporate income tax rate under the "Tax Cuts and Jobs Act" (the "Act") from accumulated other comprehensive income ("AOCI") to retained earnings. The guidance was effective January 1, 2019, with early adoption permitted. The Company elected to early adopt this guidance as of January 1, 2018 and to reclassify the stranded tax effects related to the Act, which resulted in an increase of $45 million to both retained earnings and accumulated other comprehensive loss.

Significant Accounting Policies

Financial Statements— The unaudited financial statements included herein have been prepared by Illinois Tool Works Inc. and Subsidiaries (the “Company”). In the opinion of management, the interim financial statements reflect all adjustments of a normal recurring nature necessary for a fair statement of the results for interim periods. It is suggested that these financial statements be read in conjunction with the financial statements and notes to financial statements included in the Company’s 2018 Annual Report on Form 10-K. Certain reclassifications of prior year data have been made to conform with current year reporting.

New Accounting Pronouncements

In May 2014, the Financial Accounting Standards Board (the "FASB") issued authoritative guidance to change the criteria for revenue recognition. The core principle of the new guidance is that revenue should be recognized to depict the transfer of control 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. In addition, expanded revenue disclosures are required. The Company's sales arrangements with customers are predominantly short-term in nature and generally provide for transfer of control and risks and rewards of ownership at the time of product shipment or delivery of service. As such, the timing of revenue recognition under both the prior and new guidance is the same for the majority of the Company’s transactions. Effective January 1, 2018, the Company adopted the new revenue recognition guidance under the modified retrospective method and recorded a cumulative-effect adjustment reducing retained earnings by $9 million as of January 1, 2018.

In February 2016, the FASB issued authoritative guidance to change the criteria for recognizing leasing transactions. The primary change under the new guidance is that a lessee is required to recognize a lease liability and corresponding right-of-use asset for its operating leases. The new guidance also requires additional disclosures. Effective January 1, 2019, the Company adopted the new guidance prospectively for all operating lease transactions as of and after the effective date with a noncancellable lease term greater than one year. Upon adoption, the Company recorded a lease liability of $205 million and a corresponding right-of-use asset. The new guidance did not have a material impact on the results of operations or cash flows for the three months ended March 31, 2019. Refer to Note 5. Leases for additional information regarding the Company’s lease transactions.

In October 2016, the FASB issued authoritative guidance requiring the recognition of the income tax consequences of an intra-entity transfer of an asset, other than inventory, when the transfer occurs rather than when transferred to a third party as required under the prior guidance. The provisions of the new guidance are being applied prospectively to intra-entity asset transfers on or after January 1, 2018 and may result in future tax rate volatility. Upon adoption of the new guidance on January 1, 2018, the Company recorded a cumulative-effect adjustment reducing deferred tax assets and retained earnings by $406 million.

In August 2017, the FASB issued authoritative guidance which includes targeted improvements to simplify the application of hedge accounting and improve financial reporting of hedging activities. Effective January 1, 2019, the Company adopted the new guidance which did not have a material impact on the results of operations, financial position or cash flows.

In February 2018, the FASB issued authoritative guidance which allows for an optional one-time reclassification of the stranded tax effects resulting from the change in the U.S. federal corporate income tax rate under the "Tax Cuts and Jobs Act" (the "Act") from accumulated other comprehensive income ("AOCI") to retained earnings. The guidance was effective January 1, 2019, with early adoption permitted. The Company elected to early adopt this guidance as of January 1, 2018 and to reclassify the stranded tax effects related to the Act, which resulted in an increase of $45 million to both retained earnings and accumulated other comprehensive loss.