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Investments in equity securities (Detail) - USD ($) $ in Millions | Dec. 31, 2024 | Dec. 31, 2023
--- | --- | ---
Summary of Investment Holdings [Line Items] |  |
Cost Basis | $ 75,506 | $ 109,416
Net Unrealized Gains | 196,082 | 244,426
Fair Value | 271,588 | 353,842
Banks, insurance and finance [Member] |  |
Summary of Investment Holdings [Line Items] |  |
Cost Basis | 15,707 | 27,136
Net Unrealized Gains | 75,936 | 51,176
Fair Value | 91,643 | 78,312
Consumer products [Member] |  |
Summary of Investment Holdings [Line Items] |  |
Cost Basis | 12,658 | 34,248
Net Unrealized Gains | 92,091 | 166,895
Fair Value | 104,749 | 201,143
Commercial, industrial and other [Member] |  |
Summary of Investment Holdings [Line Items] |  |
Cost Basis | 47,141 | 48,032
Net Unrealized Gains | 28,055 | 26,355
Fair Value | $ 75,196 | $ 74,387

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