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Fair value measurements - Other information (Detail)
$ in Millions
12 Months Ended
Dec. 31, 2024
USD ($)
Dec. 31, 2023
USD ($)
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Investments in equity securities $ 271,588 $ 353,842
Significant Unobservable Inputs (Level 3) [Member] | Fair Value, Measurements, Recurring [Member]    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Investments in equity securities 9,668 $ 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 8,429  
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 $ 1,234  
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 6 years  
Significant Unobservable Inputs (Level 3) [Member] | Discount for Illiquidity and Subordination | 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 0.42