Fair value measurements - Other information (Detail) $ in Millions	6 Months Ended
	Jun. 30, 2024 USD ($)		Dec. 31, 2023 USD ($)
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Investments in equity securities	$ 284,871	[1]	$ 353,842	[2]
Significant Unobservable Inputs (Level 3) [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Investments in equity securities	10,359		$ 10,474
Significant Unobservable Inputs (Level 3) [Member] | Preferred Stock [Member] | Fair Value, Measurements, Recurring [Member] | Discounted Cash Flow [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Investments in equity securities	8,441
Significant Unobservable Inputs (Level 3) [Member] | Common Stock Warrants [Member] | Fair Value, Measurements, Recurring [Member] | Warrant Pricing Model [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Investments in equity securities	$ 1,913
Significant Unobservable Inputs (Level 3) [Member] | Measurement Input, Expected Term | Weighted Average [Member] | Preferred Stock [Member] | Fair Value, Measurements, Recurring [Member] | Discounted Cash Flow [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Unobservable inputs, term	5 years
Significant Unobservable Inputs (Level 3) [Member] | Measurement Input, Expected Term | Weighted Average [Member] | Common Stock Warrants [Member] | Fair Value, Measurements, Recurring [Member] | Warrant Pricing Model [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Unobservable inputs, term	5 years
Significant Unobservable Inputs (Level 3) [Member] | Discounts for Liquidity and Subordination [Member] | Weighted Average [Member] | Preferred Stock [Member] | Fair Value, Measurements, Recurring [Member] | Discounted Cash Flow [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Unobservable inputs	0.0372
Significant Unobservable Inputs (Level 3) [Member] | Measurement Input, Option Volatility | Weighted Average [Member] | Common Stock Warrants [Member] | Fair Value, Measurements, Recurring [Member] | Warrant Pricing Model [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Unobservable inputs	0.41

[1] Approximately 72% of the aggregate fair value was concentrated in five companies (American Express Company – $35.1 billion; Apple Inc. – $84.2 billion; Bank of America Corporation – $41.1 billion; The Coca-Cola Company – $25.5 billion and Chevron Corporation – $18.6 billion).

[2] Approximately 79% of the aggregate fair value was concentrated in five companies (American Express Company – $28.4 billion; Apple Inc. – $174.3 billion; Bank of America Corporation – $34.8 billion; The Coca-Cola Company – $23.6 billion and Chevron Corporation – $18.8 billion).