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Investment in associated companies - Share in Results from Associated Companies (Details) - USD ($) $ in Millions | 6 Months Ended | 12 Months Ended
--- | --- | ---
Dec. 31, 2018 | Jul. 01, 2018 | Dec. 31, 2020 | Dec. 31, 2019
Schedule of Equity Method Investments [Line Items] |  |  |  |
Share in results from associated companies (net of tax) | $ (90) | $ 149 | $ (77) | $ (115)
Seadrill Partners |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |
Share in results from associated companies (net of tax) |  |  | (75) |
Seadrill Partners | Seadrill Partners - Direct ownership investments |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |
Share in results from associated companies (net of tax) | (82) | 77 | (75) | (107)
Seadrill Partners | Seadrill Partners - Subordinated Units |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |
Share in results from associated companies (net of tax) | (20) | 22 | 0 | (17)
Seabras Sapura |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |
Share in results from associated companies (net of tax) | 24 | 46 | 20 | 29
SeaMex |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |
Share in results from associated companies (net of tax) | (12) | 4 | (22) | (19)
Sonadrill |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |
Share in results from associated companies (net of tax) | 0 | 0 | (2) | (1)
Gulfdrill |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |
Share in results from associated companies (net of tax) | $ 0 | $ 0 | $ 2 | $ 0

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