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Authorised and issued share capital - Additional Information (Detail)
£ / shares in Units, £ in Millions
 12 Months Ended
Dec. 31, 2019
GBP (£)
shares
ADRs
yr
£ / shares
$ / ADRs
Dec. 31, 2018
GBP (£)
£ / shares
$ / ADRs
shares
Dec. 31, 2017
£ / shares
$ / ADRs
Disclosure of classes of share capital [line items]      
Share option granted in Life | yr 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    
WPP Worldwide Share Ownership Program [member]      
Disclosure of classes of share capital [line items]      
Vesting period 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    
Executive Stock Option Plan [member]      
Disclosure of classes of share capital [line items]      
Vesting period 3 years    
Share option performance effect Nine years and eight months    
Ordinary shares [member]      
Disclosure of classes of share capital [line items]      
Number of the ordinary shares of the Company held by the ESOP 9,219,837 14,820,994  
Market value of the ordinary shares of the Company held by the ESOP | £ £ 98.3 £ 125.5  
Number of ordinary shares held in treasury 70,787,730 70,854,553  
Ordinary shares held in Treasury at market value | £ £ 755.0 £ 599.9  
Average share price | £ / shares £ 9.39 £ 11.56 £ 15.86
Ordinary shares [member] | WPP Share Option Plan 2015 [member]      
Disclosure of classes of share capital [line items]      
Number of ordinary shares under option 13,413,425    
Ordinary shares [member] | WPP Executive Share Option Scheme [member]      
Disclosure of classes of share capital [line items]      
Number of ordinary shares under option 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 2,757,654    
American depository receipts [member]      
Disclosure of classes of share capital [line items]      
Average ADR Price | $ / ADRs 59.93 77.31 101.86
American depository receipts [member] | WPP Share Option Plan 2015 [member]      
Disclosure of classes of share capital [line items]      
Unexercised options | ADRs 1,396,745    
American depository receipts [member] | WPP Worldwide Share Ownership Program [member]      
Disclosure of classes of share capital [line items]      
Unexercised options | ADRs 388,854    
Share purchase options [member]      
Disclosure of classes of share capital [line items]      
Unrecognised compensation costs related to share options | £ £ 7.3 £ 8.5  
Unrecognised compensation cost related to share options, weighted average period 19 months 20 months