Gulf of Mexico oil spill - Summary of Movement in Provision (Details) - Litigation and claims - Gulf of Mexico Oil Spill - USD ($) $ in Millions	3 Months Ended	6 Months Ended
Jun. 30, 2018	Jun. 30, 2018
Reconciliation of changes in other provisions [abstract]
Beginning balance, provisions	$ 2,231	$ 2,580
Net increase in provision	411	476
Reclassified to other payables	(1,816)	(1,875)
Utilization	(401)	(756)
Ending balance, provisions	$ 425	$ 425

The increase in existing other provisions. [Refer: Other provisions]

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The increase (decrease) in other provisions resulting from transfers and changes that the entity does not separately disclose in the same statement or note. [Refer: Other provisions]

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The amount used (ie incurrent and charged against the provision) for other provisions. [Refer: Other provisions]

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The amount of liabilities of uncertain timing or the amount recognised when: (a) the entity has a present obligation (legal or constructive) as a result of a past event; (b) it is probable (ie more likely than not) that an outflow of resources embodying economic benefits will be required to settle the obligation; and (c) a reliable estimate can be made of the amount of the obligation.

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