Commitments and contingencies - Legal proceedings (Detail) - Pending litigation - item	Nov. 02, 2018	Aug. 20, 2018
Motor Oil MDL
Legal proceedings
Number of nationwide classes	2	2
Number of statewide classes		17
California Wage/Hour Litigation
Legal proceedings
Number of lawsuits	3

Number of pending claims pertaining to a loss contingency.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 450
-SubTopic 20
-Section 50
-Paragraph 4
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=82911808&loc=d3e14435-108349

Name:	us-gaap_LossContingencyPendingClaimsNumber
Namespace Prefix:	us-gaap_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant