v3.26.1
Debt - Classification and Credit Facilities (Detail)
$ in Millions, $ in Millions
6 Months Ended
Jun. 30, 2026
USD ($)
Jun. 30, 2026
CAD ($)
Dec. 31, 2025
USD ($)
Debt      
Debt maturing or subject to remarketing within twelve months $ 3,800    
Current portion of long-term debt 1,075   $ 711
Tax Exempt Bonds [Member]      
Debt      
Debt with interest rate periods that expire in the next 12 months 2,000    
Debt classified as long-term due to intent and ability to refinance on long-term basis $ 2,700    
Tax Exempt Bonds [Member] | Minimum [Member]      
Debt      
Interest rate (as a percent) 0.70% 0.70% 0.70%
Tax Exempt Bonds [Member] | Maximum [Member]      
Debt      
Interest rate (as a percent) 4.60% 4.60% 4.60%
Commercial Paper Program [Member]      
Debt      
Debt maturing or subject to remarketing within twelve months $ 1,100    
Debt term 397 days    
Commercial paper borrowings $ 1,100    
7.1% senior notes due August 2026 [Member]      
Debt      
Debt maturing or subject to remarketing within twelve months $ 223    
Interest rate (as a percent) 7.10% 7.10%  
Canadian Senior Notes maturing September 2026      
Debt      
Debt maturing or subject to remarketing within twelve months $ 352    
Interest rate (as a percent) 2.60% 2.60% 2.60%
Debt instrument face amount   $ 500  
Financing leases and other [Member]      
Debt      
Debt maturing or subject to remarketing within twelve months $ 206    
Revolving Credit Facility [Member]      
Debt      
Maximum capacity 3,500    
Outstanding borrowings under credit facility 0    
Letters of credit outstanding 226    
Unused and available credit capacity $ 2,200    
Revolving Credit Facility [Member] | Minimum [Member]      
Debt      
Spread rate (as a percent) 0.585%    
Revolving Credit Facility [Member] | Maximum [Member]      
Debt      
Spread rate (as a percent) 1.025%    
Other Letter Of Credit Lines [Member]      
Debt      
Letters of credit outstanding $ 944