XML 171 R156.htm IDEA: XBRL DOCUMENT v3.19.1
Inventories - Summary of Current Inventories (Detail) - GBP (£)
£ in Millions
Dec. 31, 2018
Dec. 31, 2017
Classes of current inventories [abstract]    
Raw materials £ 5 £ 4
Work in progress   2
Finished goods 149 142
Returns asset 10  
Inventories £ 164 £ 148