This item represents an other than temporary decline in value that has been recognized against an investment accounted for under the equity method of accounting. The excess of the carrying amount over the fair value of the investment represents the amount of the write down which is or was reflected in earnings. The written down value is a new cost basis with the adjusted value of the investment becoming its new carrying value subject to the equity accounting method. Evidence of a loss in value might include, but would not necessarily be limited to, absence of an ability to recover the carrying amount of the investment or inability of the investee to sustain an earnings capacity which would justify the carrying amount of the investment.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 323
-SubTopic 10
-Section 35
-Paragraph 32
-URI http://asc.fasb.org/extlink&oid=121548190&loc=d3e32787-111569

Name:	us-gaap_EquityMethodInvestmentOtherThanTemporaryImpairment
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

Loss on impairment of investments in 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]
Total impairment of investments in associated companies and joint ventures	$ 0	$ 0	$ 47	$ 302
Seadrill Partners
Schedule of Equity Method Investments [Line Items]
Total impairment of investments in associated companies and joint ventures			47	302
Seadrill Partners - Direct ownership investments \| Seadrill Partners
Schedule of Equity Method Investments [Line Items]
Total impairment of investments in associated companies and joint ventures	0	0	47	248
Seadrill Partners - Seadrill member interest and IDRs \| Seadrill Partners
Schedule of Equity Method Investments [Line Items]
Total impairment of investments in associated companies and joint ventures	$ 0	$ 0	$ 0	$ 54