Summary of contributions by reportable segment Disclosure of geographical areas [text block] Items that may be reclassified subsequently to profit or loss: Components of other comprehensive income that will be reclassified to profit or loss, net of tax [abstract] Amortisation and impairment of acquired intangible assets Amortization And Impairment Of Acquired Intangible Assets Amortization and impairment of acquired intangible assets. Contingent consideration liabilities Contingent Consideration Liabilities Net movement of liabilities in respect of put options Net movement of financial instruments The increase (decrease) in equity resulting from the recognition/remeasurement of financial instruments. Other costs of services and general and administrative costs Other Costs Of Services And General Administrative Costs Other Costs Of Services And General Administrative Costs Disclosure of geographical areas [line items] Disclosure of geographical areas [line items] Restructuring costs Restructuring and transformation costs Restructuring And Transformation Costs Restructuring and transformation costs. Purchases of property, plant and equipment Purchase of property, plant and equipment, classified as investing activities Non-cash share-based incentive plans (including share options) Adjustments for share-based payments Derivatives in designated hedge relationships Derivatives designated as hedges [member] Derivatives in designated hedge relationships. Other pass-through costs Other Pass Through Costs Other Pass Through Costs Disclosure of detailed information about business combination [line items] Disclosure of detailed information about business combination [line items] Acquisitions Acquisitions Classified As Investing Activities The cash flows from acquisitions classified as investing activities Total borrowings (excluding bank overdrafts) Borrowings, Excluding Bank Overdrafts Borrowings, Excluding Bank Overdrafts Increase/(decrease) in provisions Increase (decrease) in other provisions All levels of fair value hierarchy Levels of fair value hierarchy [domain] Net movemnet in non-controlling interests Increase (decrease) through acquisition of subsidiary, equity Tax on share-based payments Decrease (increase) through tax on share-based payment transactions, equity Non-controlling interests Non-controlling interests Event After Reporting Period [Abstract] Event After Reporting Period [Abstract] Reconciliation of operating profit to headline operating profit [Abstract] Reconciliation of operating profit to headline operating profit Amortisation and impairment of acquired intangible assets Adjustments for amortisation and impairment of acquired intangible assets. Amortisation and impairment of acquired intangible assets. Current liabilities Current liabilities [abstract] Classes of share capital [axis] Classes of share capital [axis] Non-controlling interests Profit (loss), attributable to non-controlling interests Earnings from associates Earnings from associates Earnings from associates Share of profit (loss) of associates accounted for using equity method Interests in associates Investments accounted for using equity method Other investments Other investments1 [Member] Other investments [member] Establishment costs Establishment Costs Establishment costs. Equity Equity [abstract] Disclosure of detailed information about financial instruments [abstract] Disclosure of detailed information about financial instruments [abstract] Condensed Cash Flow Statement [Table] Condensed Cash Flow Statement [Table] Additions Purchases, fair value measurement, liabilities Disclosure of operating segments [abstract] Disclosure of operating segments [abstract] Total equity Beginning balance Ending balance Equity Disclosure of transactions between related parties [line items] Disclosure of transactions between related parties [line items] Cash used by operations Cash flows from (used in) operations Property, plant and equipment Property, plant and equipment Movements on equity investments held at fair value through other comprehensive income Other comprehensive income, net of tax, gains (losses) from investments in equity instruments Disposals Sales, fair value measurement, assets Cash Reconciliation [Table] Cash Reconciliation [Table] Cash Reconciliation Disclosure of transactions between related parties [abstract] Disclosure of transactions between related parties [abstract] Gross profit Gross profit Share capital Classes of share capital [domain] Statement of comprehensive income [abstract] Statement of comprehensive income [abstract] Statement of changes in equity [line items] Statement of changes in equity [line items] Attributable to: Comprehensive income attributable to [abstract] Corporate bond Corporate bond [member] Corporate bond. Disclosure of basis of preparation [Line Items] Disclosure of basis of preparation [Line Items] Disclosure of basis of preparation [Line Items] Held at fair value through other comprehensive income Financial assets at fair value through other comprehensive income, category [member] Exchange adjustments Increase (Decrease) Through Net Exchange Differences Fair Value Measurement,Liabilities Increase (Decrease) Through Net Exchange Differences Fair Value Measurement,Liabilities Items that will not be reclassified subsequently to profit or loss: Components of other comprehensive income that will not be reclassified to profit or loss, net of tax [abstract] Finance and investment income Finance and investment income Finance income Level 1 Level 1 of fair value hierarchy [member] Classes of financial liabilities [axis] Classes of financial liabilities [axis] Financial liabilities, class Classes of financial liabilities [domain] Goodwill impairment Adjustments for impairment loss recognised in profit or loss, goodwill Gains recognised in other comprehensive income Gains (losses) recognised in other comprehensive income including exchange differences, fair value measurement, liabilities Provisions for liabilities and charges Provisions For Liabilities And Current Charges Provisions For Liabilities And Current Charges Disclosure of geographical areas [table] Disclosure of geographical areas [table] Level 2 Level 2 of fair value hierarchy [member] Interest paid on lease liabilities Adjustment for Interest Paid on Lease Liabilities Adjustment for Interest Paid on Lease Liabilities Trade and other payables Trade and other non-current payables Equity holders of the parent Profit (loss), attributable to owners of parent Disclosure of Dividends [line items] Disclosure of Dividends [line items] Disclosure of Dividends [line items] Share premium account Share premium [member] Statement of financial position [abstract] Statement of financial position [abstract] Costs of services and general and administrative costs Disclosure of expenses [text block] Cover [Abstract] Cover [Abstract] Contingent consideration liability payments recognised in operating activities Contingent Consideration Payments Recognized In Operating Activities Contingent Consideration Payments Recognized In Operating Activities Share repurchases and buybacks Payments to acquire or redeem entity's shares Equity holders of the parent Comprehensive income, attributable to owners of parent Cash and cash equivalents and net debt [Abstract] Cash and cash equivalents and adjusted net debt [Abstract] Cash and cash equivalents and adjusted net debt Additions Purchases, fair value measurement, assets Diluted earnings Profit (loss), attributable to ordinary equity holders of parent entity, used in calculating diluted earnings per share Contingent consideration liabilities Contingent Consideration Payable To Vendors (Earnout Agreements) [Member] Contingent Consideration Payable To Vendors (Earnout Agreements) Current liabilities Current liabilities Called-up share capital Issued capital Dividends received Dividends received Losses recognised in the income statement Gains (losses) recognised in profit or loss including exchange differences, fair value measurement, assets Deferred tax assets Deferred tax assets Non- controlling interests Non-controlling interests [member] Non-controlling interests Comprehensive income, attributable to non-controlling interests Disposals Sales, fair value measurement, liabilities Other costs of services and general and administrative costs include: Other costs of services and general and administrative costs [Abstract] Other costs of services and general and administrative costs Share premium account Share premium Corporate income tax payable Current tax liabilities, current Financing activities Cash flows from (used in) financing activities [abstract] Cash Reconciliation [Line Items] Cash Reconciliation [Line Items] Cash Reconciliation Revenue from rendering of services, related party transactions Revenue from rendering of services, related party transactions Beginning balance Ending balance Financial liabilities Total comprehensive income/(loss) for the period Comprehensive income Statement of changes in equity [abstract] Statement of changes in equity [abstract] Retrospective application and retrospective restatement [axis] Retrospective application and retrospective restatement [axis] Retained earnings Retained earnings Taxation Tax expense (income) Aggregated measurement Measurement [domain] Events after reporting period Disclosure of events after reporting period [text block] Basis of preparation Disclosure of basis of preparation of financial statements [text block] Trade and other receivables Trade and other receivables Disclosure of detailed information about financial instruments [line items] Disclosure of detailed information about financial instruments [line items] Type of restructuring and transformation cost [Domain] Type of restructuring and transformation cost [Domain] Type of restructuring and transformation cost [Domain] Document Fiscal Period Focus Document Fiscal Period Focus Analysis of cash flows Disclosure of Detailed Information About Analysis of Cash Flows Explanatory [Text Block] Disclosure of detailed information about analysis of cash flows. Fair value of corporate bonds Financial liabilities, at fair value Document Period End Date Document Period End Date Losses/(gains) on disposal of investments and subsidiaries Adjustments for gain (loss) on disposal of investments in subsidiaries, joint ventures and associates Entity's total for associates [member] Associates [domain] Maturity [axis] Maturity [axis] Settlements Settlements, fair value measurement, liabilities United Kindom UNITED KINGDOM Derivative financial assets Derivative financial assets Earnings per share [line items] Earnings per share [line items] Costs of services and general and administrative costs Costs Of Services And General And Administrative Costs Costs of services and general and administrative costs. Earnings Profit (loss), attributable to ordinary equity holders of parent entity, used in calculating basic earnings per share Amounts owed by related parties Amounts receivable, related party transactions Classes of financial instruments [axis] Classes of financial instruments [axis] Borrowings due within one year (excluding bank overdrafts) Current Borrowings, Excluding Bank Overdrafts Current Borrowings, Excluding Bank Overdrafts Other interest and similar charges paid Interest paid, classified as operating activities Goodwill Goodwill Settlements Settlements, fair value measurement, assets Revenue Revenue Associates [axis] Associates [axis] Acquisitions and disposals: Disclosure of detailed information about business combination [abstract] Disclosure Of Information About Operating Cost [line items] Disclosure Of Information About Operating Cost [line items] Disclosure of information about operating cost line items. Document Type Document Type Called-up share capital Issued capital [member] Classes of financial assets [axis] Classes of financial assets [axis] Geographical areas [axis] Geographical areas [axis] Borrowings Current borrowings Finance and investment income Adjustments for finance income Other reserves Other reserves [member] Items that will not be reclassified subsequently to profit or loss Other comprehensive income that will not be reclassified to profit or loss, net of tax Interim period amount Interim Period Amount [member] Interim period amount. Profit or loss [abstract] Profit or loss [abstract] Lease liabilities Non-current lease liabilities Amounts reclassified to profit or loss Reclassification adjustments on cash flow hedges, net of tax Earnings per share [table] Earnings per share [table] Historical restructuring programs Historical Restructuring Programs [Member] Historical Restructuring Programs Other intangible assets Intangible assets other than goodwill Borrowings by name Borrowings by name [domain] Trade and other receivables Trade receivables [member] Equity shareholders’ funds Equity attributable to owners of parent Earnings per share [abstract] Earnings per share [abstract] Summary of Cash Reconciliation Disclosure of reconciliation of cash [Table Text Block] Disclosure of reconciliation of cash Currently stated Currently stated [member] Cash and cash equivalents as presented in the consolidated balance sheet Cash and cash equivalents Cash and cash equivalents Ordinary dividends [Abstract] Ordinary dividends Components of equity [axis] Components of equity [axis] Analysis of cash flows [Abstract] Analysis of cash flows Deferred tax liabilities Deferred tax liabilities Contingent consideration liabilities Contingent Considertaion Liability [Member] Contingent Considertaion Liability Basis of accounting [Abstract] Basis of preparation [Abstract] Basis of preparation Media pass-through costs Media Pass-through Costs Media pass-through costs. Profit before taxation Profit before taxation Profit (loss) before tax Other comprehensive income/(loss) for the period Other comprehensive income/(loss) for the period Other comprehensive income Earnings per share Earnings per Share from Continuing Operations [Abstract] Earnings per Share from Continuing Operations Profit before interest and taxation Profit before interest and taxation Profit Loss Before Interest and Taxation The profit (loss) before interest and taxation. Own shares Treasury shares Treasury shares [member] Summary of related party transactions outstanding Disclosure of transactions between related parties [text block] Proportion of voting rights held in associate Proportion of voting rights held in associate United States UNITED STATES Net decrease in cash and cash equivalents Increase (decrease) in cash and cash equivalents before effect of exchange rate changes Costs of services and general and administrative costs include: Other Costs Of Services And General And Administrative Cost [abstract] Other Costs Of Services And General And Administrative Cost [abstract] Business combinations [axis] Business combinations [axis] APAC Asia Pacific [Member] Revenue less pass- through costs Revenue less pass- through costs The amount of revenue less pass-through costs. Business combinations [domain] Business combinations [domain] Current assets Current assets [abstract] Non-current assets Non-current assets [abstract] General and administrative costs General and administrative expense Financial instruments, class Classes of financial instruments [domain] Disclosure of detailed information about business combination [table] Disclosure of detailed information about business combination [table] Reserve of gains and losses on hedging instruments that hedge investments in equity instruments Reserve of gains and losses on hedging instruments that hedge investments in equity instruments Depreciation of property, plant and equipment Adjustments for depreciation expense Interest received Interest received, classified as operating activities Disclosure of Dividends [table] Disclosure of Dividends [table] Disclosure of Dividends [table] Trade and other receivables Trade and other non-current receivables Condensed Cash Flow Statements, Captions [Line Items] Condensed Cash Flow Statements, Captions [Line Items] USD bonds due March 2036 USD Bonds Due March 2036 [Member] USD Bonds Due March 2036 Cash and cash equivalents at the beginning of the period Cash and cash equivalents at end of period Cash and cash equivalents as presented in the consolidated cash flow statement Cash and cash equivalents if different from statement of financial position Other potentially issuable shares (shares) Instruments With Potential Future Dilutive Effect Not Included In Calculation Of Diluted Earnings Per Share Other potentially issuable shares. Summary of contributions by reportable segments Disclosure of operating segments [text block] Weighted average shares used in basic EPS calculation (shares) Weighted average number of ordinary shares used in calculating basic earnings per share Repayment of borrowings Repayments of borrowings, classified as financing activities Borrowings by name [axis] Borrowings by name [axis] Other investments Changes in fair value measurement, assets [abstract] Schedule of Analysis of Financial Instruments Measured at Fair Value Disclosure of fair value of financial instruments [text block] Net current liabilities Current assets (liabilities) Goodwill impairment Impairment loss recognised in profit or loss, goodwill Property-related impairment charges Adjustments for Impairment Charges Included Within Restructuring Costs Adjustments for Impairment Charges Included Within Restructuring Costs Disclosure of basis of preparation [Table] Disclosure of basis of preparation [Table] Disclosure of basis of preparation [Table] Other reserves Other reserves Other investments Equity investments [member] Summary of Costs of Service and General and Administrative Costs Disclosure of expenses by nature [text block] Investing activities Cash flows from (used in) investing activities [abstract] Related party transactions Disclosure of related party [text block] Financial assets, class Classes of financial assets [domain] Financial Instruments - fair value Disclosure of financial instruments [text block] Compas Compas [Member] Compas Borrowings, interest rate Borrowings, interest rate Net cash outflow from investing activities Cash flows from (used in) investing activities Derivative liabilities Derivatives Liabilities [member] Derivatives liabilities. Provisions for liabilities and charges Provisions For Liabilities And Non-current Charges The amount of non-current provisions other than provisions for defined benefit plans. Level 3 Level 3 of fair value hierarchy [member] Property-related impairment charges Impairment loss recognised in profit or loss, property, plant and equipment Trade and other payables Trade and other payables Non-cash share-based incentive plans (including share options) Increase (decrease) through share-based payment transactions, equity Disposals of investments and subsidiaries Disposals Of Investments And Subsidiaries Classified As Investing Activities The cash flows from disposals of investments and subsidiaries classified as investing activities. Goodwill recognised as of acquisition date Goodwill recognised as of acquisition date Net cash inflow/(outflow) from financing activities Cash flows from (used in) financing activities Staff costs Employee benefits expense (Loss)/gain on net investment hedges Gains (losses) on hedges of net investments in foreign operations, net of tax Non-current assets Non-current assets Foreign exchange differences on translation of foreign operations Other comprehensive income, net of tax, exchange differences on translation of foreign operations Decrease in working capital Increase (decrease) in working capital Current assets Current assets Losses/(gains) on disposal of investments and subsidiaries Gains (losses) on disposals of investments Own shares Treasury shares Statement of changes in equity [table] Statement of changes in equity [table] Accrued income and unbilled media Current accrued income including current contract assets Total transactions with owners Increase (decrease) through transactions with owners, equity Losses recognised in the income statement Gains (losses) recognised in profit or loss including exchange differences, fair value measurement, liabilities Operating cash flow before movements in working capital and provisions Cash flows from (used in) operations before changes in working capital Depreciation of right-of-use assets Adjustments for Right of Use Depreciation Adjustments for Right of Use Depreciation Disclosure Of Information About Operating Cost [table] Disclosure Of Information About Operating Cost [table] Disclosure of information about operating cost. Amortisation of other intangible assets Adjustments For Amortisation Of Other Intangible Assets Adjustments For Amortisation Of Other Intangible Assets Foreign exchange translation of cash and cash equivalents Effect of exchange rate changes on cash and cash equivalents Costs of services Cost of sales Derivative assets Derivatives Assets [member] Derivatives assets. Net cash outflow from operating activities Cash flows from (used in) operating activities Current Fiscal Year End Date Current Fiscal Year End Date Proceeds on disposal of property, plant and equipment Proceeds from sales of property, plant and equipment, classified as investing activities Summary of reconciliation of operating (loss)/profit to headline operating profit Reconciliation Of Operating Loss Profit To Headline Operating Profit [Table Text Block] Reconciliation Of Operating Loss Profit To Headline Operating Profit Costs of service and general and administrative costs [Abstract] Costs of service and general and administrative costs [Abstract] Costs of service and general and administrative costs Barrows North America Inc. (Barrows) Barrows North America Inc. (“Barrows”) [Member] Barrows North America Inc. (Barrows) Elevate 24 Elevate 24 [Member] Elevate 24 Non-current liabilities Non-current liabilities [abstract] Disclosure of transactions between related parties [table] Disclosure of transactions between related parties [table] Cash consideration for purchase of non-controlling interests Payments from changes in ownership interests in subsidiaries that do not result in loss of control Revaluation and retranslation of financial instruments Revaluation And Retranslation Of Financial Instruments Revaluation and retranslation of financial instruments. Disclosure of detailed information about financial instruments [table] Disclosure of detailed information about financial instruments [table] Geographical areas Geographical areas [domain] Document Fiscal Year Focus Document Fiscal Year Focus Trade and other receivables Trade and other current receivables Corporate income tax recoverable Current tax assets, current Group, Retail Capital Holdings Ltd (RCH) Group, Retail Capital Holdings Ltd (RCH) [Member] Group, Retail Capital Holdings Ltd (RCH) Adjustments for: Adjustments to reconcile profit (loss) [abstract] Summary of reconciliation between shares used in calculating basic and diluted EPS Disclosure Of Reconciliation Of Shares Used in Calculation of Basic And Diluted Earnings Per Share Explanatory [Table Text Block] Disclosure Of Reconciliation Of Shares Used in Calculation of Basic And Diluted Earnings Per Share Explanatory Other investments Investments other than investments accounted for using equity method Increase (decrease) due to changes in accounting policy Increase (decrease) due to changes in accounting policy [member] Profit for the period Profit for the period Profit (loss) Fair value (loss)/gain arising on hedging instruments Other comprehensive income, net of tax, cash flow hedges Earnings from associates Adjustments for undistributed profits of associates Beginning balance Ending balance Financial assets Corporation and overseas tax paid Income taxes paid, classified as operating activities Adjusting items within IFRS operating profit Adjusting Items Within IFRS Operating Profit Adjusting Items Within IFRS Operating Profit EMEA EMEA [Member] EMEA Amendment Flag Amendment Flag Equity Components of equity [domain] Restructuring costs Expense of restructuring activities Levels of fair value hierarchy [axis] Levels of fair value hierarchy [axis] North America North America [Member] Dividends paid Dividends recognised as distributions to owners Total equity shareholders’ funds Equity attributable to owners of parent [member] Non-current liabilities Non-current liabilities Closing exchange rate Closing foreign exchange rate Finance costs Finance costs Finance costs Taxation Adjustments for income tax expense Revaluation and retranslation of financial instruments Adjustment Revaluation and retranslation Of Financial Instruments Adjustment Revaluation and retranslation Of Financial Instruments. Type of restructuring and transformation cost [Axis] Type Of Restructuring And Transformation Cost [Axis] Type Of Restructuring And Transformation Cost LATAM Latin America [Member] Ordinary shares in issue (shares) Number of shares issued Segmental analysis Disclosure of entity's operating segments [text block] Dividends declared (pound per share) Dividends recognised as distributions to owners per share Net movement in own shares held by ESOP Trusts Net Movement In Own Shares Held By ESOP Trusts The increase (decrease) in equity resulting from net movement in own shares held by ESOP Trusts. Retained earnings Retained earnings [member] Bank overdrafts Bank overdrafts Dividends from associates Dividends received, classified as operating activities (Loss)/gain on costs of hedging Gains (losses) on cash flow hedges, net of tax Cash and cash equivalents and total borrowings Cash and Cash Equivalents and Debt Financing Explanatory [Text Block] Cash and Cash Equivalents and Debt Financing Explanatory Headline operating profit Headline Operating Profit Loss Headline operating profit/loss. Contingent consideration liabilities Changes in fair value measurement, liabilities [abstract] Entity Central Index Key Entity Central Index Key Previous period final amount Previous Period Final Amount [member] Previous period final amount. Items that may be reclassified subsequently to profit or loss Other comprehensive income that will be reclassified to profit or loss, net of tax Derivative financial liabilities Derivative financial liabilities Increase (decrease) due to changes in accounting policy required by IFRSs Increase (decrease) due to changes in accounting policy required by IFRSs [member] Amounts owed to related parties Amounts payable, related party transactions Employee benefits expense non headline staff Employee Benefits Expense Non Headline Staff Employee Benefits Expense Non Headline Staff Ordinary shares Ordinary shares [member] Previously stated Previously stated [member] Money market funds Money Market Fund [Member] Money Market Fund Earnings per share (EPS) Disclosure of earnings per share [text block] Attributable to: Profit (loss), attributable to [abstract] Trade and other payables Trade and other current payables Finance costs Adjustments for finance costs Cash flow hedges: Cash Flow Hedge [Abstract] Cash Flow Hedge Investment income Adjustments for Investment Income Adjustments for Investment Income Gains recognised in other comprehensive income Gains (losses) recognised in other comprehensive income including exchange differences, fair value measurement, assets Ordinary dividends Disclosure of dividends [text block] Financing and share issue costs Payments For Financing And Share Issue Costs Payments for financing and share issue costs. Impairment of investments in associates Adjustment For Impairment Of Investment In Associates Adjustment For Impairment Of Investment In Associates Corporate income tax recoverable Current tax assets, non-current Bond amount Notional amount Average exchange rate Average foreign exchange rate Summary of Analysis of Cash Flows Disclosure of analysis of cash flows explanatory [Table Text Block] Disclosure of analysis of cash flows. Lease liabilities Current lease liabilities Profit (loss) from operating activities Operating profit Profit (loss) from operating activities Reconciliation of profit before taxation to headline operating profit Reconciliation Of Operating Profit To Headline Operating Profit [Text Block] Reconciliation of operating profit to headline operating profit. Financing items Financing Items Financing Items Exchange adjustments Increase (Decrease) Through Net Exchange Differences Fair Value Measurement, Assets Increase (Decrease) Through Net Exchange Differences Fair Value Measurement, Assets Number of reportable segments Number of Reportable Segments Number of Reportable Segments Borrowings Borrowings due after one year Non-current portion of non-current borrowings Diluted earnings per ordinary share (pounds per share) Diluted EPS (pounds per share) Diluted earnings (loss) per share Aggregated time bands Maturity [domain] Consideration transferred, acquisition-date fair value Consideration transferred, acquisition-date fair value Employee benefit obligations Non-current provisions for employee benefits Proceeds from borrowings Proceeds from borrowings, classified as financing activities Held at fair value through profit or loss Financial instruments held at fair value through profit or loss [member] Financial instruments held at fair value through profit or loss. Right-of-use assets Right-of-use assets Principal elements of lease payments Payments of lease liabilities, classified as financing activities Acquisitions Disclosure of business combinations [text block] Percentage of voting equity interests acquired Percentage of voting equity interests acquired Net payment on borrowing related derivatives Proceeds (Repayments) Of Borrowing Related Derivatives Proceeds (Repayments) Of Borrowing Related Derivatives At Fair Value At fair value [member] Net assets Assets (liabilities) Summary of calculation of basic and diluted EPS Earnings per share [text block] Entity Registrant Name Entity Registrant Name Basic earnings per ordinary share (pounds per share) EPS (pounds per share) Basic earnings (loss) per share Measurement [axis] Measurement [axis] Dividends paid to non-controlling interests in subsidiary undertakings Dividends paid to non-controlling interests, classified as financing activities Purchases of intangible assets Purchase of intangible assets, classified as investing activities Statement of cash flows [abstract] Statement of cash flows [abstract] Weighted average shares used in diluted EPS calculation (shares) Weighted average shares used in diluted EPS calculation (shares) Weighted average number of ordinary shares used in calculating diluted earnings per share