v3.25.2
Fair value measurements - Other information (Detail)
$ in Millions
 6 Months Ended
Jun. 30, 2025
USD ($)
Dec. 31, 2024
USD ($)
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Investments in equity securities $ 267,923 $ 271,588
Significant Unobservable Inputs (Level 3) [Member] | Fair Value, Measurements, Recurring [Member]    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Investments in equity securities 9,429 $ 9,668
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 8,635  
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 $ 790  
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 4 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 0.0325  
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