Basis of Presentation (Policies)	6 Months Ended
Jun. 30, 2021
Accounting Policies [Abstract]
Basis of Accounting	The accompanying unaudited condensed consolidated financial statements have been prepared in accordance with the instructions to Form 10-Q and therefore do not include all information and footnotes required by accounting principles generally accepted in the U.S. (“U.S. GAAP”) for complete financial statements. On June 30, 2020, the Company completed the divestiture of its Business Products Group. Refer to the acquisitions, divestitures and discontinued operations footnote for more information. The Company's results of operations for the Business Products Group are reported as discontinued operations and all information related to the discontinued operations has been excluded from the notes to the condensed consolidated financial statements for all periods presented. Net income from discontinued operations for each period includes all costs that are directly attributable to these businesses and excludes certain corporate overhead costs that were previously allocated. Additionally, revenue from freight services provided by the Automotive Parts Group are grossed up and recast in continuing operations in each period because those sales are continuing with the discontinued operations after the divestiture. Except as disclosed herein, there have been no material changes in the information disclosed in the notes to the consolidated financial statements included in the Annual Report on Form 10-K of Genuine Parts Company (the “Company,” “we,” “our,” “us,” or “its”) for the year ended December 31, 2020. Accordingly, the unaudited condensed consolidated financial statements and related disclosures herein should be read in conjunction with the Company’s 2020 Annual Report on Form 10-K.
Use of Estimates	The preparation of interim financial statements requires management to make estimates and assumptions that affect the amounts reported in the unaudited condensed consolidated financial statements. Specifically, the Company makes estimates and assumptions in its unaudited condensed consolidated financial statements for inventory adjustments, the accrual of bad debts, credit losses on guaranteed loans, customer sales returns, and volume incentives earned, among others. Inventory adjustments (including adjustments for a majority of inventories that are valued under the last-in, first-out (“LIFO”) method) are accrued on an interim basis and adjusted in the fourth quarter based on the annual book to physical inventory adjustment and LIFO valuation. Reserves for bad debts, credit losses on guaranteed loans and customer sales returns are estimated and accrued on an interim basis based on a consideration of historical experience, current conditions, and reasonable and supportable forecasts. Volume incentives are estimated based upon cumulative and projected purchasing levels. In the opinion of management, all adjustments necessary for a fair presentation of the Company’s financial results for the interim periods have been made. These adjustments are of a normal recurring nature. The Company has reclassified certain prior period amounts to conform to the current period presentation.
Recent Accounting Pronouncements	Changes to U.S. GAAP are established by the Financial Accounting Standards Board (“FASB”) in the form of Accounting Standards Updates (“ASU”) to the FASB Accounting Standards Codification (“ASC”). The Company considers the applicability and impact of all ASUs and has determined that any recently adopted accounting pronouncements did not have a material impact on the Company's condensed consolidated financial statements and all recent accounting pronouncements not yet adopted are not applicable or are expected to have an immaterial impact on the Company's condensed consolidated financial statements.
Guarantees	The Company guarantees the borrowings of certain independently controlled automotive parts stores and businesses (“independents”) and certain other affiliates in which the Company has a noncontrolling equity ownership interest (“affiliates”). Presently, the independents are generally consolidated by unaffiliated enterprises that have controlling financial interests through ownership of a majority voting interest in the independents. The Company has no voting interest or equity conversion rights in any of the independents. The Company does not control the independents or the affiliates but receives a fee for the guarantees. The Company has concluded that the independents are variable interest entities, but that the Company is not the primary beneficiary. Specifically, the equity holders of the independents have the power to direct the activities that most significantly impact the entities’ economic performance including, but not limited to, decisions about hiring and terminating personnel, local marketing and promotional initiatives, pricing and selling activities, credit decisions, monitoring and maintaining appropriate inventories, and store hours. Separately, the Company concluded that the affiliates are not variable interest entities. The Company’s maximum exposure to loss as a result of its involvement with these independents and affiliates is generally equal to the total borrowings subject to the Company’s guarantees. While such borrowings of the independents and affiliates are outstanding, the Company is required to maintain compliance with certain covenants. At June 30, 2021, the Company was in compliance with all such covenants.In the event that the Company is required to make payments in connection with these guarantees, the Company would obtain and liquidate certain collateral pledged by the independents or affiliates (e.g., accounts receivable and inventory) to recover all or a substantial portion of the amounts paid under the guarantees. The Company recognizes a liability equal to current expected credit losses over the lives of the loans in the guaranteed loan portfolio, based on a consideration of historical experience, current conditions, the nature and expected value of any collateral, and reasonable and supportable forecasts. To date, the Company has had no significant losses in connection with guarantees of independents’ and affiliates’ borrowings and the current expected credit loss reserve is not material. As of June 30, 2021, there are no material guaranteed loans for which the borrower is experiencing financial difficulty and recovery is expected to be provided substantially through the operation or sale of the collateral.
Fair Value of Financial Instruments	Fair value is defined as an exit price, representing the amount that would be received to sell an asset or paid to transfer a liability in an orderly transaction between market participants. Fair value is a market-based measurement that is determined based on assumptions that market participants would use in pricing an asset or liability. Additionally, ASC 820, Fair Value Measurements, defines levels within a hierarchy based upon observable and non-observable inputs. •Level 1. Observable inputs such as quoted prices in active markets; •Level 2. Inputs, other than quoted prices in active markets, that are observable either directly or indirectly; and •Level 3. Unobservable inputs in which there is little or no market data, which require the reporting entity to develop its own assumptionsOur valuation technique is based primarily on prices and other relevant information generated by observable transactions involving identical or comparable assets or liabilities.Derivative instruments are recognized in the consolidated balance sheets at fair value and are designated as Level 2 in the fair value hierarchy. They are valued using inputs other than quoted prices, such as foreign exchange rates and yield curves. Refer to the derivatives and hedging footnote for further information. Fair value measurements of non-financial assets and non-financial liabilities are primarily used in the impairment analyses of goodwill, other intangible assets, and long-lived assets. These involve fair value measurements on a nonrecurring basis using Level 3 inputs as defined in the fair value hierarchy. The carrying amounts reflected in the consolidated balance sheets for cash and cash equivalents, trade accounts receivable, trade accounts payable, and borrowings under the line of credit approximate their respective fair values based on the short-term nature of these instruments.

Basis of Presentation (Policies)

6 Months Ended

Jun. 30, 2021

The accompanying unaudited condensed consolidated financial statements have been prepared in accordance with the instructions to Form 10-Q and therefore do not include all information and footnotes required by accounting principles generally accepted in the U.S. (“U.S. GAAP”) for complete financial statements. On June 30, 2020, the Company completed the divestiture of its Business Products Group. Refer to the acquisitions, divestitures and discontinued operations footnote for more information. The Company's results of operations for the Business Products Group are reported as discontinued operations and all information related to the discontinued operations has been excluded from the notes to the condensed consolidated financial statements for all periods presented. Net income from discontinued operations for each period includes all costs that are directly attributable to these businesses and excludes certain corporate overhead costs that were previously allocated. Additionally, revenue from freight services provided by the Automotive Parts Group are grossed up and recast in continuing operations in each period because those sales are continuing with the discontinued operations after the divestiture. Except as disclosed herein, there have been no material changes in the information disclosed in the notes to the consolidated financial statements included in the Annual Report on Form 10-K of Genuine Parts Company (the “Company,” “we,” “our,” “us,” or “its”) for the year ended December 31, 2020. Accordingly, the unaudited condensed consolidated financial statements and related disclosures herein should be read in conjunction with the Company’s 2020 Annual Report on Form 10-K.

Use of Estimates

The preparation of interim financial statements requires management to make estimates and assumptions that affect the amounts reported in the unaudited condensed consolidated financial statements. Specifically, the Company makes estimates and assumptions in its unaudited condensed consolidated financial statements for inventory adjustments, the accrual of bad debts, credit losses on guaranteed loans, customer sales returns, and volume incentives earned, among others. Inventory adjustments (including adjustments for a majority of inventories that are valued under the last-in, first-out (“LIFO”) method) are accrued on an interim basis and adjusted in the fourth quarter based on the annual book to physical inventory adjustment and LIFO valuation. Reserves for bad debts, credit losses on guaranteed loans and customer sales returns are estimated and accrued on an interim basis based on a consideration of historical experience, current conditions, and reasonable and supportable forecasts. Volume incentives are estimated based upon cumulative and projected purchasing levels. In the opinion of management, all adjustments necessary for a fair presentation of the Company’s financial results for the interim periods have been made. These adjustments are of a normal recurring nature. The Company has reclassified certain prior period amounts to conform to the current period presentation.

Recent Accounting Pronouncements

Changes to U.S. GAAP are established by the Financial Accounting Standards Board (“FASB”) in the form of Accounting Standards Updates (“ASU”) to the FASB Accounting Standards Codification (“ASC”). The Company considers the applicability and impact of all ASUs and has determined that any recently adopted accounting pronouncements did not have a material impact on the Company's condensed consolidated financial statements and all recent accounting pronouncements not yet adopted are not applicable or are expected to have an immaterial impact on the Company's condensed consolidated financial statements.

Guarantees

The Company guarantees the borrowings of certain independently controlled automotive parts stores and businesses (“independents”) and certain other affiliates in which the Company has a noncontrolling equity ownership interest (“affiliates”). Presently, the independents are generally consolidated by unaffiliated enterprises that have controlling financial interests through ownership of a majority voting interest in the independents. The Company has no voting interest or equity conversion rights in any of the independents. The Company does not control the independents or the affiliates but receives a fee for the guarantees. The Company has concluded that the independents are variable interest entities, but that the Company is not the primary beneficiary. Specifically, the equity holders of the independents have the power to direct the activities that most significantly impact the entities’ economic performance including, but not limited to, decisions about hiring and terminating personnel, local marketing and promotional initiatives, pricing and selling activities, credit decisions, monitoring and maintaining appropriate inventories, and store hours. Separately, the Company concluded that the affiliates are not variable interest entities. The Company’s maximum exposure to loss as a result of its involvement with these independents and affiliates is generally equal to the total borrowings subject to the Company’s guarantees. While such borrowings of the independents and affiliates are outstanding, the Company is required to maintain compliance with certain covenants. At June 30, 2021, the Company was in compliance with all such covenants.In the event that the Company is required to make payments in connection with these guarantees, the Company would obtain and liquidate certain collateral pledged by the independents or affiliates (e.g., accounts receivable and inventory) to recover all or a substantial portion of the amounts paid under the guarantees. The Company recognizes a liability equal to current expected credit losses over the lives of the loans in the guaranteed loan portfolio, based on a consideration of historical experience, current conditions, the nature and expected value of any collateral, and reasonable and supportable forecasts. To date, the Company has had no significant losses in connection with guarantees of independents’ and affiliates’ borrowings and the current expected credit loss reserve is not material. As of June 30, 2021, there are no material guaranteed loans for which the borrower is experiencing financial difficulty and recovery is expected to be provided substantially through the operation or sale of the collateral.

Fair Value of Financial Instruments

Fair value is defined as an exit price, representing the amount that would be received to sell an asset or paid to transfer a liability in an orderly transaction between market participants. Fair value is a market-based measurement that is determined based on assumptions that market participants would use in pricing an asset or liability. Additionally, ASC 820, Fair Value Measurements, defines levels within a hierarchy based upon observable and non-observable inputs.

•Level 1. Observable inputs such as quoted prices in active markets;

•Level 2. Inputs, other than quoted prices in active markets, that are observable either directly or indirectly; and

•Level 3. Unobservable inputs in which there is little or no market data, which require the reporting entity to develop its own assumptionsOur valuation technique is based primarily on prices and other relevant information generated by observable transactions involving identical or comparable assets or liabilities.Derivative instruments are recognized in the consolidated balance sheets at fair value and are designated as Level 2 in the fair value hierarchy. They are valued using inputs other than quoted prices, such as foreign exchange rates and yield curves. Refer to the derivatives and hedging footnote for further information. Fair value measurements of non-financial assets and non-financial liabilities are primarily used in the impairment analyses of goodwill, other intangible assets, and long-lived assets. These involve fair value measurements on a nonrecurring basis using Level 3 inputs as defined in the fair value hierarchy. The carrying amounts reflected in the consolidated balance sheets for cash and cash equivalents, trade accounts receivable, trade accounts payable, and borrowings under the line of credit approximate their respective fair values based on the short-term nature of these instruments.