Basis of Presentation (Policies)	6 Months Ended
Jun. 30, 2020
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. During the six months ended 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 (loss) 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, certain intercompany sales from the Automotive Parts Group are grossed up and recast in continuing operations in each period because those sales will continue 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, 2019. Accordingly, the unaudited interim condensed consolidated financial statements and related disclosures herein should be read in conjunction with the Company’s 2019 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 interim condensed consolidated financial statements. Specifically, the Company makes estimates and assumptions in its interim 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 ASUs to the FASB Accounting Standards Codification (“ASC”). The Company considers the applicability and impact of all ASUs and any not listed below were assessed and determined to be not applicable or are expected to have a minimal impact on the Company's condensed consolidated financial statements. Financial Instruments - Credit Losses (Topic 326) In June 2016, the FASB issued ASU 2016-13, Measurement of Credit Losses on Financial Instruments. Among other things, the ASU and its amendments replace the incurred loss impairment model for receivables and loan guarantees with a current expected credit loss model. The new model measures impairment based on expected credit losses over the remaining contractual life of an asset, considering available information about the collectability of cash flows, past events, current conditions, and reasonable and supportable forecasts. Additional quantitative and qualitative disclosures are required. The Company adopted ASU 2016-13 and its amendments as of January 1, 2020, which included recognizing a cumulative-effect adjustment to reduce opening retained earnings by $11,432, net of taxes. Compensation - Retirement Benefits (Topic 715) In August 2018, the FASB issued ASU 2018-14, Changes to the Disclosure Requirements for Defined Benefit Plans. The updated accounting guidance modifies the disclosure requirements for employers that sponsor defined benefit pension or other postretirement plans by removing, adding and clarifying certain disclosures. These provisions must be applied retrospectively. ASU 2018-14 is effective for periods beginning after December 15, 2020, with an option to adopt early. The adoption of ASU 2018-14 is not expected to have a significant impact on the Company’s financial position, results of operations or disclosures. The Company does not plan to early adopt the standard.
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, including a debt to earnings before interest, taxes, depreciation and amortization (“EBITDA”) ratio and certain limitations on additional borrowings. At June 30, 2020, 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, 2020, 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	The carrying amounts reflected in the condensed consolidated balance sheets for cash and cash equivalents, trade accounts receivable, trade accounts payable, and borrowings under the line of credit and term loan approximate their respective fair values based on the short-term nature of these instruments.The fair value of fixed rate debt is designated as Level 2 in the fair value hierarchy (i.e., significant observable inputs) and is based primarily on the discounted value of future cash flows using current market interest rates offered for debt of similar credit risk and maturity.

Basis of Presentation (Policies)

6 Months Ended

Jun. 30, 2020

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. During the six months ended 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 (loss) 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, certain intercompany sales from the Automotive Parts Group are grossed up and recast in continuing operations in each period because those sales will continue 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, 2019. Accordingly, the unaudited interim condensed consolidated financial statements and related disclosures herein should be read in conjunction with the Company’s 2019 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 interim condensed consolidated financial statements. Specifically, the Company makes estimates and assumptions in its interim 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 ASUs to the FASB Accounting Standards Codification (“ASC”). The Company considers the applicability and impact of all ASUs and any not listed below were assessed and determined to be not applicable or are expected to have a minimal impact on the Company's condensed consolidated financial statements.

Financial Instruments - Credit Losses (Topic 326)

In June 2016, the FASB issued ASU 2016-13, Measurement of Credit Losses on Financial Instruments. Among other things, the ASU and its amendments replace the incurred loss impairment model for receivables and loan guarantees with a current expected credit loss model. The new model measures impairment based on expected credit losses over the remaining contractual life of an asset, considering available information about the collectability of cash flows, past events, current conditions, and reasonable and supportable forecasts. Additional quantitative and qualitative disclosures are required. The Company adopted ASU 2016-13 and its amendments as of January 1, 2020, which included recognizing a cumulative-effect adjustment to reduce opening retained earnings by $11,432, net of taxes.

Compensation - Retirement Benefits (Topic 715)

In August 2018, the FASB issued ASU 2018-14, Changes to the Disclosure Requirements for Defined Benefit Plans. The updated accounting guidance modifies the disclosure requirements for employers that sponsor defined benefit pension or other postretirement plans by removing, adding and clarifying certain disclosures. These provisions must be applied retrospectively. ASU 2018-14 is effective for periods beginning after December 15, 2020, with an option to adopt early. The adoption of ASU 2018-14 is not expected to have a significant impact on the Company’s financial position, results of operations or disclosures. The Company does not plan to early adopt the standard.

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, including a debt to earnings before interest, taxes, depreciation and amortization (“EBITDA”) ratio and certain limitations on additional borrowings. At June 30, 2020, 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, 2020, 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

The carrying amounts reflected in the condensed consolidated balance sheets for cash and cash equivalents, trade accounts receivable, trade accounts payable, and borrowings under the line of credit and term loan approximate their respective fair values based on the short-term nature of these instruments.The fair value of fixed rate debt is designated as Level 2 in the fair value hierarchy (i.e., significant observable inputs) and is based primarily on the discounted value of future cash flows using current market interest rates offered for debt of similar credit risk and maturity.