Intangible Assets Intangible Asset and Goodwill [Table Text Block] Work in process Work in process Contract with Customer, Asset, before Allowance for Credit Loss, Current Amortization of prior service cost Other Comprehensive (Income) Loss, Defined Benefit Plan, Prior Service Cost (Credit), Reclassification Adjustment from AOCI, before Tax Portion at Fair Value Measurement [Member] Portion at Fair Value Measurement [Member] Title of 12(b) Security Title of 12(b) Security Carrying Amount Reported Value Measurement [Member] Acquisition of businesses and interests in affiliates, net of cash acquired Payments to Acquire Businesses and Interest in Affiliates Document Fiscal Year Focus Document Fiscal Year Focus Integration and acquisition related costs Business Combination, Acquisition-Related Cost, Expense Segment Reporting [Abstract] Segment Reporting [Abstract] Common stock Common Stock, Value, Issued Interest Expense Interest Expense, Operating and Nonoperating Long-Term Debt Schedule of Long-Term Debt Instruments [Table Text Block] Pension and Other Postemployment Benefits Retirement Benefits [Text Block] Public Relations Public relations [Member] Public relations [Member] Expected return on plan assets Defined Benefit Plan, Expected Return (Loss) on Plan Assets Measurement Frequency [Axis] Measurement Frequency [Axis] Common Stock, $0.15 Par Value Common Stock, $0.15 Par Value [Member] Common Stock, $0.15 Par Value [Member] Severance and Repositioning Costs [Abstract] Severance and Repositioning Costs Fair value of equity awards2 Business Combination, Consideration Transferred, Equity Interest, Directors Awards Business Combination, Consideration Transferred, Equity Interest, Directors Awards Goodwill, Dispositions Goodwill, Divestiture Goodwill, Noncontrolling interests in acquired businesses Goodwill, Acquisitions of noncontrolling interests Noncontrolling interests' share of goodwill of acquired businesses. Amendment Flag Amendment Flag Liabilities held for sale Business Combination, Recognized Liability Assumed, Liabilities Held for Sale Business Combination, Recognized Liability Assumed, Liabilities Held for Sale Current Liabilities: Liabilities, Current [Abstract] Entity Common Stock, Shares Outstanding Entity Common Stock, Shares Outstanding Acquisitions Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability, Issuances Interest paid Interest Paid, Including Capitalized Interest, Operating and Investing Activities 2.400% Senior Notes (Exchange/IPG) due 2031 2.400% Senior Notes (Exchange/IPG) due 2031 [Member] 2.400% Senior Notes (Exchange/IPG) due 2031 Property and equipment Business Combination, Recognized Asset Acquired, Property, Plant, and Equipment €600 million 3.850% Senior Notes due 2034 3.850% Euro Note due 2034 [Member] 3.850% Euro Note due 2034 Other Comprehensive Income (Loss): Other Comprehensive Income (Loss), Net of Tax [Abstract] Assets held for sale Business Combination, Recognized Asset Acquired, Assets Held for Sale Business Combination, Recognized Asset Acquired, Assets Held for Sale Acquisition of additional noncontrolling interests Payments to Noncontrolling Interests Net Increase (Decrease) in Cash and Cash Equivalents Cash, Cash Equivalent, Restricted Cash, and Restricted Cash Equivalent, Period Increase (Decrease), Including Exchange Rate Effect and Discontinued Operation [Abstract] Entity Address, State or Province Entity Address, State or Province Foreign currency translation adjustment Other Comprehensive Income (Loss), Foreign Currency Transaction and Translation Adjustment, Net of Tax Assets: Assets, Fair Value Disclosure [Abstract] Intangible Assets, net of accumulated amortization of $1,101.4 and $903.2 Intangible Asset, Excluding Goodwill, after Accumulated Amortization Basic Weighted Average Number of Shares Outstanding, Basic Goodwill, accumulated impairment losses Goodwill, Impaired, Accumulated Impairment Loss Fair Value, by Balance Sheet Grouping [Table] Fair Value, by Balance Sheet Grouping [Table] Number of Reportable Segments Number of Reportable Segments Total Current Liabilities Liabilities, Current Customer advances Disposal Group, Including Discontinued Operation, Deferred Revenue, Current Contingent purchase price obligations Contingent Purchase Price Obligations [Member] Contingent Purchase Price Obligations [Member] Customer Relationships Customer Relationships [Member] IPG IPG [Member] IPG EMEA EMEA [Member] Entity Address, City or Town Entity Address, City or Town Supplemental Financial Information and Non-Cash Increases in Lease Liabilities Schedule of Cash Flow, Supplemental Disclosures [Table Text Block] Reportable Segment Reportable Segment [Member] Reportable Segment Other purchased and internally developed software Software, Internally Developed and Purchased [Member] Statement of Financial Position [Abstract] Statement of Financial Position [Abstract] Purchase Consideration [Abstract] Business Combination, Consideration Transferred [Abstract] Class of Stock [Axis] Class of Stock [Axis] Intangible assets, Net Carrying Value Intangible Asset, Finite-Lived, after Accumulated Amortization Fair Value [Abstract] Fair Value [Abstract] Fair Value [Abstract] Proceeds from stock plans Proceeds from Stock Plans Level 2 Fair Value, Inputs, Level 2 [Member] Intangible assets, accumulated amortization Intangible assets, Accumulated Amortization Intangible Asset, Finite-Lived, Accumulated Amortization Work in process Disposal Group, Including Discontinued Operation, Inventory, Current Credit Facilities, maximum borrowing capacity Line of Credit Facility, Maximum Borrowing Capacity Other Comprehensive Income (Loss) Other comprehensive income (loss) Other Comprehensive Income (Loss), Net of Tax Income Taxes [Abstract] Income Taxes [Abstract] Income Taxes [Abstract] United States UNITED STATES Long-Term Debt [Abstract] Notes Payable, by Type, Current and Noncurrent [Abstract] Schedule of Long-Term Debt Instruments [Table] Schedule of Long-Term Debt Instruments [Table] Supplemental Cash Flow Data [Abstract] Supplemental Cash Flow Data [Abstract] Supplemental Cash Flow Data [Abstract] Treasury stock, at cost Treasury Stock, Value Other current liabilities Business Combination, Recognized Liability Assumed, Other Liability, Current Segment Revenue, Segment Operating Expenses and Segment Operating Income of our Operating Segments Segment Reporting [Table Text Block] Noncontrolling Interests Noncontrolling Interest [Member] Income tax effect Other Comprehensive (Income) Loss, Defined Benefit Plan, after Reclassification Adjustment, Tax Changes in Contingent Purchase Price Obligations Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Table Text Block] Intangible assets Business Combination, Recognized Asset Acquired, Identifiable Intangible Asset, Excluding Goodwill Short-Term Borrowings [Abstract] Short-Term Debt [Abstract] Media and production costs Media, Production and Other Costs Media and production costs accrued and incurred on behalf of customers that are billed during the production process in accordance with the terms of the client contract. Document Period End Date Document Period End Date Change in Operating Capital [Abstract] Adjustment to Reconcile Net Income to Cash Provided by (Used in) Operating Activity, Increase (Decrease) in Operating Capital [Abstract] Net Cash Provided By (Used in) Investing Activities Cash Provided by (Used in) Investing Activity, Including Discontinued Operation Unrecognized tax benefits Unrecognized Tax Benefits Liabilities held for sale Total Liabilities Held for Sale or Disposition Disposal Group, Including Discontinued Operation, Liabilities, Current Equity Method Investments Business Combination, Recognized Asset Acquired, Equity Method Investments Business Combination, Recognized Asset Acquired, Equity Method Investments Accumulated Other Comprehensive Income (Loss) Equity [Text Block] Security Exchange Name Security Exchange Name Long-term debt Business Combination, Recognized Liability Assumed, Long-Term Debt, Noncurrent Reconciliation of Segment Operating Income to Income Before Income Taxes and Income From Equity Method Investments Segment Reporting, Reconciliation of Other Item by Segment to Consolidated [Table Text Block] Net change in noncontrolling interests Noncontrolling Interest, Period Increase (Decrease) Debt [Abstract] Debt [Abstract] Debt [Abstract] Supplemental Cash Flow Data Cash Flow, Supplemental Disclosures [Text Block] Accumulated other comprehensive income (loss) Accumulated Other Comprehensive Income (Loss), Net of Tax Entity Shell Company Entity Shell Company Consolidation Items [Domain] Consolidation Items [Domain] Revaluation and interest Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability, Gain (Loss) Included in Earnings Statement of Comprehensive Income [Abstract] Statement of Comprehensive Income [Abstract] Net Income per Share Earnings Per Share [Text Block] Unbilled fees and costs and contract assets Unbilled Contracts Receivable Net Income Per Share - Omnicom Group Inc.: Earnings Per Share [Abstract] Document Fiscal Period Focus Document Fiscal Period Focus Trading Symbol Trading Symbol Geographical [Domain] Geographical [Domain] Capital expenditures Payments to Acquire Property, Plant, and Equipment 2.600% Senior Notes due 2031 2.60% Senior Notes due 2031 [Member] 2.60% Senior Notes due 2031 Preliminary Purchase Price Allocation Business Combination, Recognized Asset Acquired and Liability Assumed [Table Text Block] Dividends paid to noncontrolling interest shareholders Payments of Ordinary Dividends, Noncontrolling Interest Reclassification from AOCI, Current Period, Net of Tax, Attributable to Parent Reclassification from AOCI, Current Period, Net of Tax, Attributable to Parent Technology and Other Technology and Other [Member] Technology and Other Net Income per Share - Omnicom Group Inc.: Earnings Per Share, Diluted [Abstract] Defined Benefit Pension Plans and Postemployment Arrangements Accumulated Defined Benefit Plans Adjustment Attributable to Parent [Member]  Long-Term Debt, Gross Long-Term Debt, Gross (Decrease) in customer advances, taxes payable and other current liabilities Increase (Decrease) in customer advances and other current liabilities Increase (Decrease) in customer advances and other current liabilities Integrated Media Integrated Media [Member] Integrated Media Depreciation and amortization Depreciation, Depletion and Amortization, Nonproduction Cash Flows From Operating Activities: Cash Provided by (Used in) Operating Activity, Including Discontinued Operation [Abstract] Accounts payable Disposal Group, Including Discontinued Operation, Accounts Payable, Current Common Stock, shares Shares, Issued Diluted Diluted Weighted Average Number of Shares Outstanding, Diluted Geographic Markets [Member] Geographic Markets [Member] Geographic Markets Disaggregation of Revenue [Line Items] Disaggregation of Revenue [Line Items] Commitments and Contingent Liabilities [Abstract] Commitments and Contingent Liabilities [Abstract] Commitments and Contingent Liabilities [Abstract] Entity Emerging Growth Company Entity Emerging Growth Company Fair value of net assets acquired Business Combination, Recognized Asset Acquired to Liability Assumed, Excess (Less) Property and Equipment at cost, less accumulated depreciation of $1,253.7 and $1,386.8 Property, Plant, and Equipment and Finance Lease Right-of-Use Asset, after Accumulated Depreciation and Amortization Commercial Paper [Member] Commercial Paper [Member] Acquired intangible assets and internally developed strategic platform assets Acquired intangible assets and internally developed strategic platform assets [Member] Acquired intangible assets and internally developed strategic platform assets Experiential & Other Experiential [Member] Experiential [Member] Disposal Groups, Including Discontinued Operations Disposal Groups, Including Discontinued Operations [Table Text Block] 4.200% Senior Notes due 2030 4.20% Senior Notes due 2030 [Member] 4.20% Senior Notes due 2030 Short-term debt Short-Term Debt Third-party service costs Third-party service costs Third-party service costs Employer contributions Defined Benefit Plan, Plan Assets, Contributions by Employer Dilutive stock options and restricted shares Weighted Average Number of Shares Outstanding, Diluted, Adjustment Property and Equipment, accumulated depreciation Property, Plant, and Equipment and Finance Lease Right-of-Use Asset, Accumulated Depreciation and Amortization Change in other assets and liabilities, net Increase (Decrease) in Other Operating Assets and Liabilities, Net Treasury Stock Treasury Stock, Common [Member] (Increase) decrease in work in process and other current assets Increase (Decrease) in work in progress and other current assets Increase (Decrease) in work in progress and other current assets Intangible Asset, Goodwill and Other [Abstract] Intangible Asset, Goodwill and Other [Abstract] Share-based compensation APIC, Share-Based Payment Arrangement, Increase for Cost Recognition Level 1 Fair Value, Inputs, Level 1 [Member] Effective tax rate Effective Income Tax Rate Reconciliation, Percent Revenue [Abstract] Revenue [Abstract] Revenue [Abstract] Long-Term Debt Long-Term Debt, Fair Value Net Periodic Benefit Expense Schedule of Net Benefit Costs [Table Text Block] 3.375% Senior Notes (Exchange/IPG) due 2041 3.375% Senior Notes (Exchange/IPG) due 2041 [Member] 3.375% Senior Notes (Exchange/IPG) due 2041 Depreciation and amortization of right-of-use assets Depreciation Accounts receivable Disposal Group, Including Discontinued Operation, Accounts, Notes and Loans Receivable, Net Operating Lease Right-Of-Use Assets Operating Lease, Right-of-Use Asset Pension and other postemployment benefits: Other Comprehensive (Income) Loss, Defined Benefit Plan, after Reclassification Adjustment, after Tax [Abstract] Changes in Accumulated Other Comprehensive Income (Loss) AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward] Short-term debt Business Combination, Recognized Liability Assumed, Short-term Debt Business Combination, Recognized Liability Assumed, Short-term Debt Basic and Diluted Net Income per Share Schedule of Earnings Per Share, Basic and Diluted [Table Text Block] Change in temporary equity Change in temporary equity Changes in temporary equity during the period. Debt Instrument, Name [Domain] Debt Instrument, Name [Domain] 3.600% Senior Notes due 2026 3.60% Senior Notes due 2026 [Member] 3.60% Senior Notes due 2026 Segment Reporting Segment Reporting [Text Block] Dividends paid to common shareholders Payments of Ordinary Dividends, Common Stock Disaggregation of Revenue Disaggregation of Revenue [Table Text Block] Amortization of Intangible Assets Intangible Asset, Finite-Lived, Amortization Expense [Table Text Block] Weighted Average Shares: Weighted Average Shares (millions): Weighted Average Number of Shares Outstanding Reconciliation [Abstract] Operating lease right-of-use assets Business Combination, Recognized Asset Acquired, Operating Lease Right-of-Use Assets Business Combination, Recognized Asset Acquired, Operating Lease Right-of-Use Assets Cash and cash equivalents Cash and Cash Equivalents, Fair Value Disclosure Americas Americas [Member] Total Equity Beginning Balance Ending Balance Equity, Including Portion Attributable to Noncontrolling Interest Business Combination [Line Items] Business Combination [Line Items] Net periodic benefit expense Defined Benefit Plan, Net Periodic Benefit Cost (Credit) Other assets Disposal Group, Including Discontinued Operation, Other Assets, Current Accounts receivable Business Combination, Recognized Asset Acquired, Receivable, Current Accumulated Other Comprehensive Income (Loss) [Line Items] Accumulated Other Comprehensive Income (Loss) [Line Items] Accumulated Other Comprehensive Income [Abstract] Accumulated Other Comprehensive Income (Loss) [Abstract] Accumulated Other Comprehensive Income (Loss) [Abstract] Unamortized deferred loss from settlement of interest rate swap Deferred Gain (Loss) on Discontinuation of Interest Rate Fair Value Hedge Unamortized discount Debt Instrument, Unamortized Discount (Premium), Net Restructuring Cost [Table] Restructuring Cost [Table] Cash Flows From Investing Activities: Cash Provided by (Used in) Investing Activity, Including Discontinued Operation [Abstract] Fair Value, Recurring [Member] Fair Value, Recurring [Member] Real estate Facility Closing [Member] Share Repurchase Program, Authorized, Amount Share Repurchase Program, Authorized, Amount Segment Reporting [Line Items] Segment Reporting [Line Items] Document Quarterly Report Document Quarterly Report Segments [Domain] Segments [Domain] Europe Europe [Member] Effect of foreign exchange rate changes on cash and cash equivalents Effect of Exchange Rate on Cash, Cash Equivalent, Restricted Cash, and Restricted Cash Equivalent, Including Discontinued Operation Income Before Income Taxes and Income (Loss) From Equity Method Investments Income (Loss) from Continuing Operations before Equity Method Investments, Income Taxes, Noncontrolling Interest Income (Loss) from Continuing Operations before Equity Method Investments, Income Taxes, Noncontrolling Interest Debt Debt Disclosure [Text Block] Advertising Advertising [Member] Repayment of debt Repayment of debt Repayments of Long-Term Debt Severance and repositioning costs, after-tax Severance and repositioning costs, after-tax Severance and repositioning costs, after-tax Severance and Repositioning Costs Restructuring and Related Costs [Table Text Block] Equity Method Investments Equity Method Investments Severance and repositioning, liability, beginning balance Severance and repositioning, liability, beginning balance Restructuring Reserve Business Combination [Table] Business Combination [Table] Equity Component [Domain] Equity Component [Domain] Credit Facilities, covenant compliance Line of Credit Facility, Covenant Compliance Credit Facilities [Abstract] Line of Credit Facility [Abstract] 3.700% Senior Notes due 2032 €600 million 3.700% Senior Notes due 2032 3.70% Senior Notes due 2032 [Member] 3.70% Senior Notes due 2032 Total Operating Expenses Costs and Expenses Long-term debt, interest rate Debt Instrument, Interest Rate, Stated Percentage Common stock dividends declared Dividends, Common Stock, Cash Total Shareholders’ Equity January 1 June 30 Equity, Attributable to Parent Other Assets Business Combination, Recognized Asset Acquired, Other Asset, Noncurrent Restructuring Type [Axis] Restructuring Type [Axis] Marketable equity securities Equity Securities, FV-NI, Current Presentation of Financial Statements [Abstract] Presentation of Financial Statements [Abstract] Presentation of Financial Statements [Abstract] ASSETS: Assets [Abstract] Omnicom shares issued, IPG acquisition Business Combination, Consideration Transferred, Equity Interest, Share Issued, Number of Shares Other, net Proceeds from (Payment for) Other Financing Activity Accounts receivable, allowance for doubtful accounts Accounts Receivable, Allowance for Credit Loss, Current Changes in Contingent Purchase Price Obligations [Roll Forward] Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward] Selling, general and administrative expenses Selling, General and Administrative Expense Consolidated Balance Sheets (Parenthetical) [Abstract] Consolidated Balance Sheets (Parenthetical) [Abstract] Consolidated Balance Sheets (Parenthetical) [Abstract] 4.200% Senior Notes due 2029 4.200% Senior Note due 2029 [Member] 4.200% Senior Note due 2029 Other current assets Disposal Group, Including Discontinued Operation, Prepaid and Other Assets, Current Type of Restructuring [Domain] Type of Restructuring [Domain] Business Combination [Domain] Business Combination [Domain] Revenue and Long-Lived Assets and Goodwill by Geographic Region Segment Reporting, Entity-Wide Information Not Provided as Part of Reportable Segment, Geographical Area, Revenue and Long-Lived Asset [Line Items] Commitments and Contingent Liabilities Commitments and Contingencies Disclosure [Text Block] Anti-dilutive stock options and restricted shares (millions) Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount Change in Goodwill Goodwill [Table Text Block] Entity Central Index Key Entity Central Index Key 4.650% Senior Notes (Exchange/IPG) due 2028 4.650% Senior Notes (Exchange/IPG) due 2028 [Member] 4.650% Senior Notes (Exchange/IPG) due 2028 Components of Net Periodic Benefit Expense Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract] Additional paid-in capital Additional Paid in Capital, Common Stock Current portion of debt Long-term debt, current portion Notes Payable, Current Other, net Adjustment to Reconcile Net Income to Cash Provided by (Used in) Operating Activity, Other Item Business Combination [Axis] Business Combination [Axis] Net Cash Provided by (Used In) Operating Activities Cash Provided by (Used in) Operating Activity, Including Discontinued Operation Income Statement [Abstract] Income Statement [Abstract] Shareholders’ Equity: Equity, Attributable to Parent [Abstract] Document Transition Report Document Transition Report Fair Value Hierarchy and NAV [Axis] Fair Value Hierarchy and NAV [Axis] Net Income per Share [Abstract] Net Income per Share [Abstract] Net Income per Share [Abstract] Entity Listings [Line Items] Entity Listings [Line Items] Revenue and Long-Lived Assets and Goodwill by Geographic Region Segment Reporting, Entity-Wide Information Not Provided as Part of Reportable Segment, Geographical Area, Revenue and Long-Lived Asset [Table Text Block] Other current Assets Business Combination, Recognized Asset Acquired, Other Asset, Current City Area Code City Area Code Accumulated Other Comprehensive Income (Loss) AOCI Attributable to Parent [Member] Subsequent Events Subsequent Events [Text Block] Entity Listings [Table] Entity Listings [Table] Fair value of shares issued to IPG shareholders1 Business Combination, Consideration Transferred, Equity Interest Statement [Line Items] Statement [Line Items] TOTAL ASSETS Assets Business Combination [Abstract] Accelerated Share Repurchase [Abstract] Accelerated Share Repurchase [Abstract] Amortization of prior service cost Defined Benefit Plan, Amortization of Prior Service Cost (Credit) Operating Segments Operating Segments [Member] Revenue, entities classified as held for sale Disposal Group, Including Discontinued Operation, Revenue Non-marketable equity securities Equity Securities without Readily Determinable Fair Value, Amount Total Liabilities and Non-controlling interest Business Combination, Recognized Liability Assumed, Liability Long-term liability - operating leases Business Combination, Recognized Liability Assumed, Lease Obligation Other comprehensive income (loss) before reclassifications OCI, before Reclassifications, Net of Tax, Attributable to Parent Commercial paper, maximum amount outstanding Line of Credit Facility, Maximum Amount Outstanding During Period Measurement Basis [Axis] Measurement Basis [Axis] Long-Term Liabilities Other Liabilities, Noncurrent Goodwill Goodwill, January 1 Goodwill, June 30 Goodwill Retirement Plan Type [Axis] Retirement Plan Type [Axis] Work in process Business Combination, Recognized Asset Acquired, Inventory, Current 0.800% Senior Notes due 2027 €500 million 0.800% Senior Notes due 2027 0.80% Senior Notes due 2027 [Member] 0.80% Senior Notes due 2027 [Member] Accounts payable Business Combination, Recognized Liability Assumed, Accounts Payable, Current Retained Earnings Retained Earnings [Member] Long-Term Liability - Operating Leases Operating Lease, Liability, Noncurrent Taxes payable Taxes Payable, Current Credit Facility [Member] Revolving Credit Facility [Member] Non-controlling interests Business Combination, Recognized Liability Assumed, Noncontrolling Interest Business Combination, Recognized Liability Assumed, Noncontrolling Interest Cash and Cash equivalents Business Combination, Recognized Asset Acquired, Cash and Cash Equivalent 5.375% Senior Notes (Exchange/IPG) due 2033 5.375% Senior Notes (Exchange/IPG) due 2033 [Member] 5.375% Senior Notes (Exchange/IPG) due 2033 Foreign Currency Translation Accumulated Foreign Currency Adjustment Attributable to Parent [Member] Carrying Amount and Fair Value of Financial Assets and Liabilities Fair Value, by Balance Sheet Grouping [Table Text Block] Diluted Earnings Per Share, Diluted Accumulated Other Comprehensive Income (Loss) [Table] Accumulated Other Comprehensive Income (Loss) [Table] Entity Current Reporting Status Entity Current Reporting Status Net Cash Provided by (Used In) Financing Activities Cash Provided by (Used in) Financing Activity, Including Discontinued Operation Other current liabilities Disposal Group, Including Discontinued Operation, Other Liabilities, Current Use of operating capital Increase (decrease) in operating capital Adjustment to Reconcile Net Income to Cash Provided by (Used in) Operating Activity, Increase (Decrease) in Operating Capital Liabilities: Liabilities, Fair Value Disclosure [Abstract] 5.300% Senior Notes due 2036 5.300% Senior Note due 2036 [Member] 5.300% Senior Note due 2036 Amortization of intangible assets Intangible Asset, Finite-Lived, Amortization Expense Severance and Repositioning Costs Severance and Repositioning Costs [Text Block] Severance and Repositioning Costs Intangible assets: Intangible Asset, Finite-Lived [Line Items] 4.750% Senior Notes (Exchange/IPG) due 2030 4.750% Senior Notes (Exchange/IPG) due 2030 [Member] 4.750% Senior Notes (Exchange/IPG) due 2030 Adjustments to reconcile net income to net cash used in operating activities: Adjustment to Reconcile Net Income to Cash Provided by (Used in) Operating Activity [Abstract] Total Assets Business Combination, Recognized Asset Acquired, Asset Cash Flows From Financing Activities: Cash Provided by (Used in) Financing Activity, Including Discontinued Operation [Abstract] Interest cost Defined Benefit Plan, Interest Cost Goodwill, Contingent purchase price obligations of acquired businesses Goodwill, Contingent Purchase Price of Acquired Businesses Goodwill, Contingent Purchase Price of Acquired Businesses Contract Terminations and Other Contract Termination [Member] Assets held for sale Total Assets Held for Sale or Disposition Disposal Group, Including Discontinued Operation, Assets, Current Accelerated Share Repurchase Accelerated Share Repurchase [Text Block] Accelerated Share Repurchase Intangible Asset, Finite-Lived, Class [Axis] Intangible Asset, Finite-Lived, Class [Axis] Credit Facilities, covenant terms Line of Credit Facility, Covenant Terms Goodwill and Intangible Assets Intangible Asset and Goodwill [Text Block] Comprehensive Income Attributed To Noncontrolling Interests Comprehensive Income (Loss), Net of Tax, Attributable to Noncontrolling Interest Fair Value Estimate of Fair Value Measurement [Member] Revenue Revenue from Contract with Customer [Text Block] Foreign currency derivatives Foreign Currency Contracts, Liability, Fair Value Disclosure Accelerated Share Repurchases, Settlement (Payment) or Receipt Accelerated Share Repurchases, Settlement (Payment) or Receipt Other, net Payment for (Proceeds from) Other Investing Activity Segment Reporting [Table] Segment Reporting [Table] Property and Equipment, net Disposal Group, Including Discontinued Operation, Property, Plant, and Equipment, Current Uncommitted credit lines [Member] Uncommitted lines of credit [Member] Uncommitted lines of credit [Member] Other current assets Other Assets, Current January 1 June 30 Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability Value Income tax effect Other Comprehensive Income (Loss), Cash Flow Hedge, Gain (Loss), Reclassification, Tax Operating Income Operating Income (Loss) Remaining performance obligation, contracts greater than one year Revenue, Remaining Performance Obligation, Amount Asia-Pacific Asia Pacific [Member] Current Fiscal Year End Date Current Fiscal Year End Date Loss on assets held for sale and dispositions Gain (Loss) on Disposition of Business Cash flow hedge: Other Comprehensive Income (Loss), Cash Flow Hedge, Gain (Loss), after Reclassification and Tax [Abstract] Business Combinations Business Combination [Text Block] Severance and repositioning, liability, rollforward Restructuring Reserve [Roll Forward] Dividends Declared Per Common Share Common Stock, Dividends, Per Share, Declared Entity File Number Entity File Number Service cost Defined Benefit Plan, Service Cost Change in short-term debt Proceeds from (Repayments of) Short-Term Debt Stock issued, share-based compensation Shares Issued, Value, Share-Based Payment Arrangement, after Forfeiture Dividends to noncontrolling interests Noncontrolling Interest, Decrease from Distributions to Noncontrolling Interest Holders Amortization of loss included in interest expense Other Comprehensive Income (Loss), Cash Flow Hedge, Gain (Loss), Reclassification, before Tax Proceeds from assets held for sale Proceeds from Divestiture of Interest in Subsidiaries and Affiliates Pension and Other Postemployment Benefits [Abstract] Pension and Other Postemployment Benefits [Abstract] Pension and Other Postemployment Benefits [Abstract] Equity Components [Axis] Equity Components [Axis] (Increase) decrease in accounts receivable Increase (Decrease) in Accounts Receivable Product and Service [Domain] Product and Service [Domain] Disaggregation of Revenue [Table] Disaggregation of Revenue [Table] Entity Interactive Data Current Entity Interactive Data Current Net Income Attributed To Noncontrolling Interests Net Income (Loss) Attributable to Noncontrolling Interest Deferred Tax Liabilities Deferred Income Tax Liabilities, Net Entity Small Business Entity Small Business Comprehensive Income - Omnicom Group Inc. Comprehensive Income (Loss), Net of Tax, Attributable to Parent Decrease in accounts payable Increase (Decrease) in Accounts Payable, Trade Subsequent Events [Abstract] Subsequent Events [Abstract] Payments Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability, Settlements 5.300% Senior Notes due 2034 5.30% Senior Notes due 2034 [Member] 5.30% Senior Notes due 2034 Pension plans and other postemployment benefits, net of tax Other Comprehensive (Income) Loss, Defined Benefit Plan, after Reclassification Adjustment, after Tax Other current liabilities Other Liabilities, Current Health Health Care [Member] Other Assets Other Assets, Noncurrent Document Type Document Type Customer advances Business Combination, Recognized Liability Assumed, Deferred Revenue, Current Statement of Stockholders' Equity [Abstract] Proceeds from borrowings Proceeds from Issuance of Long-Term Debt Local Phone Number Local Phone Number Postemployment Arrangements [Member] Other Postretirement Benefits Plan [Member] Consolidation Items [Axis] Consolidation Items [Axis] Entity Address, Postal Zip Code Entity Address, Postal Zip Code Entity Registrant Name Entity Registrant Name Commitments and Contingent Liabilities (Note 13) Commitments and Contingencies Credit Facilities, expiration date Line of Credit Facility, Expiration Date Intangible assets, Gross Carrying Value Intangible Asset, Finite-Lived, before Accumulated Amortization Revenue Revenues Income (Loss) From Equity Method Investments Income (Loss) from Equity Method Investments Changes in Goodwill Goodwill [Roll Forward] LIABILITIES AND EQUITY: Liabilities and Equity [Abstract] Intangible Asset, Finite-Lived, Class [Domain] Intangible Asset, Finite-Lived, Class [Domain] Trade Names Trade Names [Member] Financial Assets and Liabilities Measured at Fair Value on a Recurring Basis Schedule of Fair Value, Assets and Liabilities Measured on Recurring Basis [Table Text Block] Fair Value Fair Value Disclosures [Text Block] Level 3 Fair Value, Inputs, Level 3 [Member] Cash flow hedge, net of tax Other Comprehensive Income (Loss), Cash Flow Hedge, Gain (Loss), Reclassification, after Tax Treasury Stock, Shares, Acquired Treasury Stock, Shares, Acquired 2.450% Senior Notes due 2030 2.45% Senior Notes due 2030 [Member] 2.45% Senior Notes due 2030 Geographical [Axis] Geographical [Axis] 1.400% Senior Notes due 2031 €500 million 1.400% Senior Notes due 2031 1.40% Senior Notes due 2031 [Member] 1.40% Senior Notes due 2031 Cash Flow Hedge Accumulated Gain (Loss), Net, Cash Flow Hedge, Parent [Member] Income taxes paid Income Tax Paid, before Refund Received Payment of contingent purchase price obligations Payment for Contingent Consideration Liability, Financing Activities Discipline [Member] Discipline [Member] Discipline Entity Tax Identification Number Entity Tax Identification Number Assets Acquired [Abstract] Business Combination, Recognized Asset Acquired, Asset [Abstract] Liability Class [Axis] Liability Class [Axis] Long-Term Debt, including current portion Notes Payable Common stock repurchased Treasury Stock, Value, Acquired, Cost Method Repositioning Liabilities, Payments Payments for Restructuring Cash and cash equivalents Cash and Cash Equivalents at the Beginning of Period Cash and Cash Equivalents at the End of Period Cash, Cash Equivalent, Restricted Cash, and Restricted Cash Equivalent, Continuing Operation Schedule of Finite-Lived Intangible Assets [Table] Intangible Asset, Finite-Lived [Table] Entity Incorporation, State or Country Code Entity Incorporation, State or Country Code Presentation of Financial Statements Organization, Consolidation and Presentation of Financial Statements Disclosure [Text Block] Comprehensive Income Comprehensive Income (Loss), Net of Tax, Including Portion Attributable to Noncontrolling Interest Measurement Frequency [Domain] Measurement Frequency [Domain] Debt Instrument [Axis] Debt Instrument [Axis] Long-term liabilities Business Combination, Recognized Liability Assumed, Other Liability, Noncurrent Cash paid for fractional shares Payments to Acquire Businesses, Gross Share-based compensation Share-Based Payment Arrangement, Noncash Expense Long-lived assets and goodwill Long-lived Assets and Goodwill Long-lived Assets and Goodwill Basic Earnings Per Share, Basic Repurchases of common stock Payments for Repurchase of Common Stock Customer advances Contract with Customer, Liability, Current Total Current Assets Assets, Current Third-party incidental costs Third-party incidental costs Third-party incidental costs Short-term debt Short-Term Debt, Fair Value Accounts receivable, net of allowance for doubtful accounts of $10.6 and $11.9 Accounts Receivable, after Allowance for Credit Loss, Current Retained earnings Retained Earnings (Accumulated Deficit) Product and Service [Axis] Product and Service [Axis] Defined Benefit Pension Plans [Member] Pension Plan [Member] Common Stock Common Stock [Member] Contingent purchase price obligations Business Combination, Contingent Consideration, Liability Fair Value Measurement [Domain] Fair Value Measurement [Domain] Severance Employee Severance [Member] Cross currency swaps - net investment hedge Derivative Instruments in Hedges, Net Investment in Foreign Operations, Assets, Fair Value Cover page. Cover [Abstract] Temporary Equity - Redeemable Noncontrolling Interests Redeemable Noncontrolling Interest, Equity, Fair Value Goodwill, Foreign currency translation Goodwill, Foreign Currency Translation, Gain (Loss) TOTAL LIABILITIES AND EQUITY Liabilities and Equity Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] Segment Reporting, Entity-Wide Information Not Provided as Part of Reportable Segment, Geographical Area, Revenue and Long-Lived Asset [Table] Segment Reporting, Entity-Wide Information Not Provided as Part of Reportable Segment, Geographical Area, Revenue and Long-Lived Asset [Table] Noncontrolling interests Equity, Attributable to Noncontrolling Interest Segments [Axis] Segments [Axis] Severance and repositioning costs Severance and repositioning, expense Restructuring Charges Total severance and contract terminations and other Total severance and contract terminations and other [Member] Total severance and contract terminations and other Purchase consideration Business Combination, Consideration Transferred, Equity Interest [Table Text Block] Shareholders’ Equity Parent [Member] Euro Commercial Paper [Member] Euro Commercial Paper [Member] Euro Commercial Paper Commercial paper, average amount outstanding Line of Credit Facility, Average Outstanding Amount Equity: Equity, Including Portion Attributable to Noncontrolling Interest [Abstract] Loss on Assets Held for Sale or Dispositions of Subsidiaries Loss on Assets Held for Sale or Dispositions of Subsidiaries [Text Block] Loss on Assets Held for Sale or Dispositions of Subsidiaries Fair Value by Liability Class [Domain] Fair Value by Liability Class [Domain] 2.250% Senior Notes due 2033 £325 million 2.250% Senior Notes due 2033 2.25% Senior Notes due 2033 [Member] 2.25% Senior Notes due 2033 Preferred stock Preferred Stock, Value, Issued Change in Operating Capital Cash Flow, Operating Capital [Table Text Block] Class of Stock [Domain] Class of Stock [Domain] Restructuring Cost and Reserve [Line Items] Restructuring Cost and Reserve [Line Items] Occupancy and other costs Occupancy and Other Costs Occupancy and other costs consist of the indirect costs related to the delivery of services, including office and equipment rent, other occupancy costs, technology costs, general office expenses and other expenses. Statement of Cash Flows [Abstract] Statement of Cash Flows [Abstract] Income Taxes Income Tax Disclosure [Text Block] Accounts payable Accounts Payable, Current Fair Value, Measurements, Fair Value Hierarchy [Domain] Fair Value Hierarchy and NAV [Domain] Goodwill, Acquisitions* Goodwill, Acquisitions Of Controlling Interests Goodwill, Acquisitions Of Controlling Interests Total Consideration Business Combination, Consideration Transferred Retirement Plan Type [Domain] Retirement Plan Type [Domain] Middle East and Africa Middle East and Africa [Member] Middle East and Africa [Member] Additional Paid-in Capital Additional Paid-in Capital [Member] Entity Filer Category Entity Filer Category Goodwill, impairment losses Goodwill, Impairment Loss Net Income Net Income Net Income (Loss), Including Portion Attributable to Noncontrolling Interest Finance leases, Net increase in lease liability Right-of-Use Asset Obtained in Exchange for Finance Lease Liability Unrecognized tax benefits that would impact effective tax rate Unrecognized Tax Benefits that Would Impact Effective Tax Rate Current Assets: Assets, Current [Abstract] Amortization of actuarial losses Other Comprehensive Income (Loss), Defined Benefit Plan, Gain (Loss), Reclassification Adjustment from AOCI, before Tax Entity Address, Address Line One Entity Address, Address Line One Operating leases, Net increase in lease liability Right-of-Use Asset Obtained in Exchange for Operating Lease Liability 5.000% Senior Notes due 2033 5.000% Senior Note due 2033 [Member] 5.000% Senior Note due 2033 North America North America [Member] Credit Facilities, amount outstanding Line of Credit Facility, Fair Value of Amount Outstanding Income Tax Expense Income Tax Expense (Benefit) Latin America Latin America [Member] Cost of services Segment cost of services Cost of Product and Service Sold Net Increase (Decrease) in Cash and Cash Equivalents Cash, Cash Equivalent, Restricted Cash, and Restricted Cash Equivalent, Period Increase (Decrease), Including Exchange Rate Effect and Discontinued Operation Long-Term Debt Notes Payable, Noncurrent Deferred tax liabilities, net Business Combination, Recognized Liability Assumed, Deferred Tax Liability Amortization of actuarial losses Defined Benefit Plan, Amortization of Gain (Loss) Net Income - Omnicom Group Inc. Net Income - Omnicom Group Inc. Net Income (Loss) Attributable to Parent Loss on Assets Held for Sale or Dispositions of Subsidiaries [Abstract] Loss on Assets Held for Sale or Dispositions of Subsidiaries Unamortized debt issuance costs Unamortized Debt Issuance Expense 5.400% Senior Notes (Exchange/IPG) due 2048 5.400% Senior Notes (Exchange/IPG) due 2048 [Member] 5.400% Senior Notes (Exchange/IPG) due 2048 Statement [Table] Statement [Table] Segment Reporting, Reconciling Item Segment Reporting, Reconciling Item, Excluding Corporate Nonsegment [Member] Salary and service costs Salary and service costs Salary and service costs are primarily comprised of employee compensation related costs. Changes in Accumulated Other Comprehensive Income (Loss) Schedule of Accumulated Other Comprehensive Income (Loss) [Table Text Block] Interest Income Investment Income, Interest Liabilities Assumed [Abstract] Business Combination, Recognized Liability Assumed, Liability [Abstract] Contract Balances Contract with Customer, Contract Asset, Contract Liability, and Receivable [Table Text Block] Foreign currency translation Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability, Gain (Loss) Included in Other Comprehensive Income (Loss) Defined Benefit Plans and Other Postretirement Benefit Plans Disclosures [Table] Defined Benefit Plans and Other Postretirement Benefit Plans Disclosures [Table] Redeemable non-controlling interest Business Combination, Recognized Liability Assumed, Redeemable Noncontrolling Interest Business Combination, Recognized Liability Assumed, Redeemable Noncontrolling Interest Salary and related costs Salary and related costs Salary and related costs