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Authorised and issued share capital - Additional Information (Detail)
 12 Months Ended
Dec. 31, 2018
USD ($)
Years
Dec. 31, 2018
GBP (£)
shares
ADRs
Years
Dec. 31, 2017
USD ($)
Dec. 31, 2017
GBP (£)
shares
Dec. 31, 2016
USD ($)
Dec. 31, 2016
GBP (£)
Disclosure of classes of share capital [line items]            
Share option performance effect Nine years and eight months Nine years and eight months        
Share option granted in Life | Years 10 10        
WPP Share Option Plan 2015 [member] | Bottom of range [member]            
Disclosure of classes of share capital [line items]            
Threshold period for employment participation in employee stock ownership plan 2 years 2 years        
WPP Worldwide Share Ownership Program [member]            
Disclosure of classes of share capital [line items]            
Vesting period 3 years 3 years        
WPP Worldwide Share Ownership Program [member] | Bottom of range [member]            
Disclosure of classes of share capital [line items]            
Threshold period for employment participation in employee stock ownership plan 2 years 2 years        
Executive Stock Option Plan [member]            
Disclosure of classes of share capital [line items]            
Vesting period 3 years 3 years        
Ordinary shares [member]            
Disclosure of classes of share capital [line items]            
Number of the ordinary shares of the Company held by the ESOP | shares   14,820,994   14,232,910    
Market value of the ordinary shares of the Company held by the ESOP | £   £ 125,500,000   £ 190,900,000    
Number of ordinary shares held in treasury | shares   70,854,553   62,578,938    
Ordinary shares held in Treasury at market value | £   £ 599,900,000   £ 839,200,000    
Number of ordinary shares under option   24,218,615   20,985,441    
Average share price | £   £ 11.56   £ 15.86   £ 16.45
Ordinary shares [member] | WPP Executive Share Option Scheme [member]            
Disclosure of classes of share capital [line items]            
Number of ordinary shares under option | shares   6,741        
Ordinary shares [member] | WPP Worldwide Share Ownership Program [member]            
Disclosure of classes of share capital [line items]            
Number of ordinary shares under option | shares   3,187,979        
Ordinary shares [member] | WPP Share Option Plan 2015 [member]            
Disclosure of classes of share capital [line items]            
Number of ordinary shares under option   18,691,100   14,602,950    
Ordinary shares [member] | WPP Worldwide Share Ownership Program [member]            
Disclosure of classes of share capital [line items]            
Number of ordinary shares under option   5,520,774   6,375,750    
American depository receipts [member]            
Disclosure of classes of share capital [line items]            
Average ADR Price | $ $ 77.31   $ 101.86   $ 111.20  
American depository receipts [member] | WPP Worldwide Share Ownership Program [member]            
Disclosure of classes of share capital [line items]            
Unexercised options | ADRs   466,559        
American depository receipts [member] | WPP Share Option Plan 2015 [member]            
Disclosure of classes of share capital [line items]            
Unexercised options | ADRs   1,286,670        
Share purchase options [member]            
Disclosure of classes of share capital [line items]            
Unrecognised compensation costs related to share options | £   £ 8,500,000   £ 9,000,000    
Unrecognised compensation cost related to share options, weighted average period 20 months 20 months 20 months 20 months