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Accounting policies (Details) - USD ($) $ in Millions | 4 Months Ended | 6 Months Ended | 12 Months Ended
--- | --- | --- | ---
Dec. 31, 2020 | Dec. 31, 2018 | Jul. 01, 2018 | Dec. 31, 2020 | Dec. 31, 2019
Property, Plant and Equipment [Line Items] |  |  |  |  |
Write off of unamortized debt discount | $ 87 | $ 0 | $ 0 | $ 87 | $ 0
Threshold percentage for recognizing actuarial gains and losses | 10.00% |  |  | 10.00% |
Overhauls of drilling units |  |  |  |  |
Property, Plant and Equipment [Line Items] |  |  |  |  |
Estimated economic useful life |  |  |  | 5 years |
Drilling units |  |  |  |  |
Property, Plant and Equipment [Line Items] |  |  |  |  |
Estimated economic useful life |  |  |  | 30 years |
Period within which management is actively committed to a probable sale of assets classified as held for sale |  |  |  | 1 year |
Equipment | Minimum |  |  |  |  |
Property, Plant and Equipment [Line Items] |  |  |  |  |
Estimated economic useful life |  |  |  | 3 years |
Equipment | Maximum |  |  |  |  |
Property, Plant and Equipment [Line Items] |  |  |  |  |
Estimated economic useful life |  |  |  | 5 years |

X
- Definition Threshold percentage for recognizing actuarial gains and losses when the net cumulative unrecognized actuarial gains or losses for each individual plan at the end of the previous reporting year exceed the higher of the present value of the defined benefit obligation and the fair value of plan assets at that date. + References No definition available. + Details
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- Definition Period within which management is actively committed to a probable sale of assets classified as held for sale. + References No definition available. + 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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- Definition Useful life of long lived, physical assets used in the normal conduct of business and not intended for resale, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days. Examples include, but not limited to, land, buildings, machinery and equipment, office equipment, furniture and fixtures, and computer equipment. + References No definition available. + Details
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