XML 109 R72.htm IDEA: XBRL DOCUMENT v3.19.1
Accounting policies - Summary of Estimated Useful Life of Property, Plant and Equipment (Detail)
 12 Months Ended
Dec. 31, 2018
Freehold buildings [member]  
Disclosure of detailed information about property, plant and equipment [line items]  
Property, plant and equipment, estimated useful life 50 years
Leasehold land and buildings [member]  
Disclosure of detailed information about property, plant and equipment [line items]  
Property, plant and equipment, estimated useful life Over the term of the lease or life of the asset, if shorter.
Bottom of range [member] | Fixtures, fittings and equipment [Member]  
Disclosure of detailed information about property, plant and equipment [line items]  
Property, plant and equipment, estimated useful life 3 years
Bottom of range [member] | Computer equipment [member]  
Disclosure of detailed information about property, plant and equipment [line items]  
Property, plant and equipment, estimated useful life 3 years
Top of range [member] | Fixtures, fittings and equipment [Member]  
Disclosure of detailed information about property, plant and equipment [line items]  
Property, plant and equipment, estimated useful life 10 years
Top of range [member] | Computer equipment [member]  
Disclosure of detailed information about property, plant and equipment [line items]  
Property, plant and equipment, estimated useful life 5 years