Investments in equity securities - Narrative (Detail) - USD ($) $ / shares in Units, $ in Billions	12 Months Ended
Dec. 31, 2022	Aug. 04, 2022
American Express Company [Member]
Summary of Investment Holdings [Line Items]
Investment owned, percent of common shares outstanding	20.40%
Occidental Petroleum Corporation [Member] \| Investment Commitment [Member]
Summary of Investment Holdings [Line Items]
Number of common shares that can be purchased	83,860,000
Exercise price for warrants, per share	$ 59.62
Warrants exercisable period after redemption of preferred stock	1 year
Occidental Petroleum Corporation [Member] \| Occidental Common Stock [Member] \| Minimum [Member]
Summary of Investment Holdings [Line Items]
Equity method investment ownership percentage		20.00%
Occidental Petroleum Corporation [Member] \| Cumulative Perpetual Preferred Stock [Member] \| Investment Commitment [Member]
Summary of Investment Holdings [Line Items]
Investment in preferred stock, liquidation value	$ 10
Investment in preferred stock, stated dividend rate	8.00%
Investment in preferred stock, redemption year start	2029
Investment in preferred stock, redemption price percentage of liquidation preference	105.00%
Investment in preferred stock, mandatory redemption price percentage of liquidation preference	110.00%

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- Definition

Investment owned percent of common shares outstanding.

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Liquidation value of preferred shares.

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Preferred stock investment mandatory redemption price percentage of liquidation preference.

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Percentage price of liquidation value at which a preferred stock investment can be redeemed by the issuer.

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- Definition

Exercise price per share or per unit of warrants or rights outstanding.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section 50
-Paragraph 3
-URI https://asc.fasb.org/extlink&oid=126973232&loc=d3e21475-112644

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- Definition

Number of securities into which the class of warrant or right may be converted. For example, but not limited to, 500,000 warrants may be converted into 1,000,000 shares.

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- Definition

The percentage of ownership of common stock or equity participation in the investee accounted for under the equity method of accounting.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 323
-SubTopic 10
-Section 50
-Paragraph 3
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- Definition

The percentage rate used to calculate dividend payments on preferred stock.

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Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section 50
-Paragraph 13
-Subparagraph (b)
-URI https://asc.fasb.org/extlink&oid=126973232&loc=SL123496158-112644

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