v3.26.1
Investments in equity securities - Narrative (Detail)
$ / shares in Units, $ in Billions
 6 Months Ended 12 Months Ended
Jun. 30, 2026
USD ($)
Company
$ / shares
shares
Dec. 31, 2025
Company
Summary of Investment Holdings [Line Items]    
Investment, Type [Extensible Enumeration] us-gaap:USTreasuryBillSecuritiesMember us-gaap:USTreasuryBillSecuritiesMember
American Express Company [Member]    
Summary of Investment Holdings [Line Items]    
Investment owned, common shares outstanding | shares 151,600,000  
Investment owned, percent of common shares outstanding 22.50%  
Equity Securities [Member] | Investment Concentration [Member] | American Express Company, Apple Inc., Bank of America Corporation, The Coca-Cola Company and Chevron Corporation [Member]    
Summary of Investment Holdings [Line Items]    
Number of holdings in concentration percentage | Company   5
Concentration percentage   65.00%
Equity Securities [Member] | Investment Concentration [Member] | Alphabet Inc, American Express Company, Apple Inc, Bank Of America Corporation and The Coca-Cola Company [Member]    
Summary of Investment Holdings [Line Items]    
Number of holdings in concentration percentage | Company 5  
Concentration percentage 66.00%  
Occidental Petroleum Corporation [Member] | Investment Commitment [Member]    
Summary of Investment Holdings [Line Items]    
Investment in preferred stock, liquidation value | $ $ 8.5  
Number of common shares that can be purchased | shares 83,900,000  
Exercise price for warrants, per share | $ / shares $ 59.59  
Investment in preferred stock, stated dividend rate 8.00%  
Investment, Type [Extensible Enumeration] Cumulative Perpetual Preferred Stock [Member]  
Investment in preferred stock, redemption year start 2029  
Investment in preferred stock, redemption price percentage of liquidation value 105.00%  
Warrants exercisable period after the date preferred stock is fully redeemed 1 year