v3.25.4
Pension plans - Fair value of plan assets (Detail) - Pension Plans, Defined Benefit [Member] - USD ($)
$ in Millions
Dec. 31, 2025
Dec. 31, 2024
Dec. 31, 2023
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets $ 13,593 $ 14,180 $ 13,379
Cash and Short-term Investments [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 2,061 600  
Equity Securities [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 6,171 9,757  
Fixed Maturity Securities [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 2,951 1,747  
Investment Funds and Other [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 2,410 2,076  
Quoted Prices (Level 1) [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 9,791 10,930  
Quoted Prices (Level 1) [Member] | Cash and Short-term Investments [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 1,983 556  
Quoted Prices (Level 1) [Member] | Equity Securities [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 5,402 9,036  
Quoted Prices (Level 1) [Member] | Fixed Maturity Securities [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 2,172 953  
Quoted Prices (Level 1) [Member] | Investment Funds and Other [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 234 385  
Significant Other Observable Inputs (Level 2) [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 1,558 1,563  
Significant Other Observable Inputs (Level 2) [Member] | Cash and Short-term Investments [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 78 44  
Significant Other Observable Inputs (Level 2) [Member] | Equity Securities [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 621 581  
Significant Other Observable Inputs (Level 2) [Member] | Fixed Maturity Securities [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 779 794  
Significant Other Observable Inputs (Level 2) [Member] | Investment Funds and Other [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 80 144  
Significant Unobservable Inputs (Level 3) [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 172 163  
Significant Unobservable Inputs (Level 3) [Member] | Equity Securities [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 148 140  
Significant Unobservable Inputs (Level 3) [Member] | Investment Funds and Other [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 24 23  
Investments Carried at Net Asset Value [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 2,072 1,524  
Investments Carried at Net Asset Value [Member] | Investment Funds and Other [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets $ 2,072 $ 1,524