Investments in equity securities - Narrative (Detail) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended
Mar. 31, 2023	Aug. 04, 2022
American Express Company [Member]
Summary of Investment Holdings [Line Items]
Investment owned, common shares outstanding	151,600,000
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	$ 9,500
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 value	105.00%
Liquidation value of mandatory redemption notifications	$ 474
Investment in preferred stock, mandatory redemption price percentage of liquidation value	110.00%

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

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

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