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Investment in associated companies - Additional Information (Details) shares in Thousands | Feb. 28, 2021 vessel rig | Dec. 31, 2020 subsidiary drilling_unit class_of_stock vessel equity_instrument drillship rig shares | Dec. 31, 2019 | Aug. 31, 2019 | Dec. 31, 2018 | Jul. 01, 2018
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Schedule of Equity Method Investments [Line Items] |  |  |  |  |  |
Number of leased rigs |  | 3 |  |  |  |
Seadrill Partners |  |  |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |  |  |
Number of drilling units | drilling_unit |  | 11 |  |  |  |
Number of drillships | drillship |  | 4 |  |  |  |
Number of semi-submersible rigs |  | 4 |  |  |  |
Number of tender rigs |  | 3 |  |  |  |
Number categories of equity instruments | equity_instrument |  | 3 |  |  |  |
Number of classes of stock | class_of_stock |  | 2 |  |  |  |
Common units outstanding (in shares) | shares |  | 7,500 |  |  |  |
Seadrill Operating LP |  |  |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |  |  |
Ownership percentage |  | 56.00% |  |  |  |
Number of rigs |  | 1 |  |  |  |
Seadrill Deepwater Drillship And Seadrill Mobile Units (Nigeria) |  |  |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |  |  |
Ownership percentage |  | 44.00% |  |  |  |
Number of rigs |  | 1 |  |  |  |
Fintech |  |  |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |  |  |
Ownership percentage |  | 50.00% |  |  |  |
Sapura Energy |  |  |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |  |  |
Ownership percentage |  | 50.00% |  |  |  |
Gulf Drilling International |  |  |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |  |  |
Ownership percentage |  | 50.00% |  |  |  |
Sonangol | Subsequent Event |  |  |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |  |  |
Ownership percentage | 50.00% |  |  |  |  |
Seadrill Partners |  |  |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |  |  |
Ownership percentage |  | 18.00% |  |  |  |
Number of investments in operating subsidiaries | subsidiary |  | 4 |  |  |  |
Seadrill Operating LP |  |  |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |  |  |
Ownership percentage |  | 42.00% |  |  |  |
Number of rigs |  | 4 |  |  |  |
Seadrill Capricorn Holdings LLC |  |  |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |  |  |
Ownership percentage |  | 49.00% |  |  |  |
Number of rigs |  | 4 |  |  |  |
Seadrill Deepwater Drillship Ltd |  |  |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |  |  |
Ownership percentage |  | 39.00% |  |  |  |
Seadrill Mobile Units (Nigeria) Ltd |  |  |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |  |  |
Ownership percentage |  | 49.00% |  |  |  |
SeaMex |  |  |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |  |  |
Number of drilling units |  | 5 |  |  |  |
Ownership percentage |  | 50.00% | 50.00% |  | 50.00% | 50.00%
Seabras Sapura |  |  |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |  |  |
Ownership percentage |  | 50.00% | 50.00% |  |  |
Number of pipe-laying service vessels | vessel |  | 6 |  |  |  |
Gulfdrill |  |  |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |  |  |
Ownership percentage |  | 50.00% | 50.00% | 50.00% | 0.00% | 0.00%
Number of premium jack-ups |  | 5 |  |  |  |
Gulfdrill | Seadrill Limited |  |  |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |  |  |
Number of leased rigs |  | 3 |  |  |  |
Gulfdrill | Third Party |  |  |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |  |  |
Number of leased rigs |  | 2 |  |  |  |
Sonadrill |  |  |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |  |  |
Ownership percentage |  | 50.00% | 50.00% |  | 0.00% | 0.00%
Sonadrill | Subsequent Event |  |  |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |  |  |
Number of drillships | 4 |  |  |  |  |
Ownership percentage | 50.00% |  |  |  |  |
Number of units bareboated by each joint venture partner | vessel | 2 |  |  |  |  |
Seadrill Partners - Subordinated Units | Seadrill Partners |  |  |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |  |  |
Ownership percentage |  | 100.00% |  |  |  |
Investment (in shares) | shares |  | 1,600 |  |  |  |
Seadrill Partners - Common Units | Seadrill Partners |  |  |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |  |  |
Ownership percentage |  | 35.00% |  |  |  |
Investment (in shares) | shares |  | 2,500 |  |  |  |
Seadrill Partners - IDRs | Seadrill Partners |  |  |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |  |  |
Ownership percentage |  | 100.00% |  |  |  |

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