Marketable securities - Marketable Securities Held (Details) - USD ($) $ in Millions	Jun. 30, 2019	Dec. 31, 2018
Gain (Loss) on Securities [Line Items]
Marketable Securities	$ 22	$ 57
Seadrill Partners - Common units
Gain (Loss) on Securities [Line Items]
Marketable Securities	9	45
Archer
Gain (Loss) on Securities [Line Items]
Marketable Securities	$ 13	$ 12

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

No definition available.

Name:	us-gaap_ScheduleOfGainLossOnInvestmentsIncludingMarketableSecuritiesAndInvestmentsHeldAtCostIncomeStatementReportedAmountsSummaryLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration