Redeemable non-controlling interest - Schedule of Changes in Redeemable Non-controlling Interest (Details) - Redeemable non-controlling interest - Asia Offshore Drilling Ltd - USD ($) $ in Millions	6 Months Ended	12 Months Ended
Dec. 31, 2018	Jul. 01, 2018	Dec. 31, 2019
Increase (Decrease) in Temporary Equity [Roll Forward]
Beginning balance	$ 30	$ 0	$ 38
Reclassification from non-controlling interest		150
Fair value adjustment on initial recognition		(127)
Net loss attributable to redeemable non-controlling interest	(1)	2	(2)
Fresh start fair value adjustment		5
Fair value adjustment	9		21
Ending balance	$ 38	$ 30	$ 57

Fresh-Start Adjustment, Increase (Decrease), Stockholders' Equity Attributable to Noncontrolling Interest

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- Definition

Temporary Equity, Fair Value Adjustment

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- Definition

A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

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- Definition

The difference between the carrying amount of a financial instrument subject to a registration payment arrangement recorded as temporary equity prior to adoption of FSP EITF 00-19-2 and the carrying amount reclassified to permanent equity upon the adoption of FSP EITF 00-19-2. Recorded as a cumulative effect adjustment to the beginning balance of retained earnings. Does not apply to registration payment arrangements that are no longer outstanding upon adoption of FSP EITF 00-19-2.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 40
-Section 50
-Paragraph 3
-URI http://asc.fasb.org/extlink&oid=6445032&loc=d3e90193-114008

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 480
-SubTopic 10
-Section S99
-Paragraph 3A
-URI http://asc.fasb.org/extlink&oid=65877616&loc=SL6540498-122764

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- Definition

Carrying amount, attributable to parent and noncontrolling interests, of an entity's issued and outstanding stock which is not included within permanent equity. Temporary equity is a security with redemption features that are outside the control of the issuer, is not classified as an asset or liability in conformity with GAAP, and is not mandatorily redeemable. Includes any type of security that is redeemable at a fixed or determinable price or on a fixed or determinable date or dates, is redeemable at the option of the holder, or has conditions for redemption which are not solely within the control of the issuer. Includes stock with a put option held by an ESOP and stock redeemable by a holder only in the event of a change in control of the issuer.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.27(b))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

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- Definition

Redemption of temporary equity as the result of a triggering event associated with the temporary equity.

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- Definition

The portion of net income or loss attributable to temporary equity interest.

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