v3.26.1
Fair value measurements - Other information (Detail)
$ in Millions
 3 Months Ended
Mar. 31, 2026
USD ($)
Dec. 31, 2025
USD ($)
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Investments in equity securities $ 288,034 $ 297,778
Significant Unobservable Inputs (Level 3) [Member] | Fair Value, Measurements, Recurring [Member]    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Investments in equity securities 10,739 $ 9,536
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 8,825  
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 $ 1,907  
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 0.43