Inventories - Additional Information (Detail) - GBP (£)	12 Months Ended
Dec. 31, 2017	Dec. 31, 2016
Classes of current inventories [abstract]
Cost of inventories relating to continuing operations recognised as expense	£ 324,000,000	£ 340,000,000
Inventory provisions charged in income statement	38,000,000	£ 48,000,000
Inventories pledged as security	£ 0

The amount of inventories recognised as an expense during the period. [Refer: Inventories]

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Name IAS
-Number 2
-IssueDate 2017-01-01
-Paragraph 36
-Subparagraph d
-URI http://eifrs.ifrs.org/eifrs/XBRL?type=IAS&num=2&date=2017-03-01&anchor=para_36_d&doctype=Standard
-URIDate 2017-03-09

Name:	ifrs-full_CostOfInventoriesRecognisedAsExpenseDuringPeriod
Namespace Prefix:	ifrs-full_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration