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Disposals Including Business Closures - Additional Information (Detail)
12 Months Ended
Oct. 05, 2017
Dec. 31, 2015
Penguin Random House [member]    
Disclosure of disposals [line items]    
Proportion of sales of voting power held in associate 22.00%  
Proportion of voting power held in associate 25.00%  
The Economist [member]    
Disclosure of disposals [line items]    
Percentage share held in Economist   10.00%