Fair value measurements - Significant unobservable inputs (Detail) - Significant Unobservable Inputs (Level 3) [Member] - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Equity Index Put Option Contract Liabilities [Member]
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Derivative contract liabilities - Beginning Balance			$ (1,065)
Derivative contract liabilities - Gains (losses) included in earnings			$ 966
Fair Value, Liability, Recurring Basis, Unobservable Input Reconciliation, Gain (Loss), Statement of Income or Comprehensive Income [Extensible Enumeration]			Nonoperating Gains (Losses)
Derivative contract liabilities - Transfers out of Level 3			$ 99
Equity Securities [Member]
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning Balance	$ 12,169	$ 11,480	8,978
Gains (losses) included in earnings	$ (40)	$ 689	$ 1,902
Fair Value, Asset, Recurring Basis, Unobservable Input Reconciliation, Gain (Loss), Statement of Income or Comprehensive Income [Extensible Enumeration]	Nonoperating Gains (Losses)	Nonoperating Gains (Losses)	Nonoperating Gains (Losses)
Acquisitions, dispositions and settlements	$ (1,661)		$ 1,100
Transfers out of Level 3			(500)
Ending Balance	$ 10,468	$ 12,169	$ 11,480

Amount of transfers of financial instrument classified as a liability out of level 3 of the fair value hierarchy.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 820
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (c)(3)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482106/820-10-50-2

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Amount of gain (loss) recognized in income from asset measured at fair value on recurring basis using unobservable input (level 3).

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 820
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (c)(1)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482106/820-10-50-2

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Amount of purchases, (sales), issuances and (settlements) of financial instrument classified as an asset measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
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Amount of transfers of financial instrument classified as an asset out of level 3 of the fair value hierarchy.

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Fair value of financial instrument classified as an asset measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing.

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Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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Amount of gain (loss) recognized in income from liability measured at fair value on recurring basis using unobservable input (level 3).

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