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Marketable securities - Gross Realized Gains and Losses Related to Marketable Securities (Details) - USD ($) $ in Millions | 6 Months Ended | 12 Months Ended
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Dec. 31, 2018 | Jul. 01, 2018 | Dec. 31, 2020 | Dec. 31, 2019
Gain (Loss) on Securities [Line Items] |  |  |  |
Total unrealized gain (loss) on marketable securities | $ (64) | $ (3) | $ (3) | $ (46)
Seadrill Partners - Common Units - unrealized loss on marketable securities |  |  |  |
Gain (Loss) on Securities [Line Items] |  |  |  |
Total unrealized gain (loss) on marketable securities | (45) | (5) | (2) | (43)
Archer - unrealized (loss)/gain on marketable securities |  |  |  |
Gain (Loss) on Securities [Line Items] |  |  |  |
Total unrealized gain (loss) on marketable securities | $ (19) | $ 2 | $ (1) | $ (3)

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- Definition Amount of unrealized gain (loss) on investment in marketable security. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 220 -SubTopic 10 -Section S99 -Paragraph 2 -Subparagraph (SX 210.5-03(7)(c)) -URI http://asc.fasb.org/extlink&oid=120395209&loc=SL114868664-224227 + Details
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- Definition 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. + References No definition available. + Details
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