Valuation and qualifying accounts (Tables)

12 Months Ended

Dec. 31, 2018

SEC Schedule, 12-09, Valuation and Qualifying Accounts [Abstract]

Summary of valuation and qualifying accounts

															$ million
							2018				2017				2016
	Not credit-impaired		Credit impaired		Trade and other receivables		Fixed asset investments		Trade and other receivables		Fixed asset investments		Trade and other receivables		Fixed asset investments
At 1 January – IAS 39	—		335		335		314		392		335		447		435
Adjustment on adoption of IFRS 9	115		—		115		(85	)	—		—		—		—
At 1 January – IFRS 9	115		335		450		229		392		335		447		435
Charged to costs and expenses	(26	)	56		30		10		68		47		120		55
Charged to other accountsa	—		(12	)	(12	)	(1	)	13		3		(7	)	(2	)
Deductions	—		(52	)	(52	)	(3	)	(138	)	(71	)	(168	)	(153	)
At 31 December	89		327		416		235		335		314		392		335

^a Principally exchange adjustments.