Debt - Classification and Credit Facilities (Detail) - USD ($)	9 Months Ended
	Sep. 30, 2025	Dec. 31, 2024
Debt
Debt maturing or subject to remarketing within twelve months	$ 3,900,000,000
Debt classified as long-term due to intent and ability to refinance on long-term basis	3,000,000,000
Current portion of long-term debt	880,000,000	$ 1,359,000,000
Tax Exempt Bonds [Member]
Debt
Debt maturing or subject to remarketing within twelve months	188,000,000
Debt with interest rate periods that expire in the next 12 months	$ 1,500,000,000
Tax Exempt Bonds [Member] | Minimum [Member]
Debt
Interest rate (as a percent)	0.70%	0.70%
Tax Exempt Bonds [Member] | Maximum [Member]
Debt
Interest rate (as a percent)	4.60%	4.60%
Commercial Paper Program [Member]
Debt
Debt maturing or subject to remarketing within twelve months	$ 861,000,000
Debt term	397 days
Commercial paper borrowings	$ 861,000,000,000
0.750% senior notes due November 2025 [Member]
Debt
Debt maturing or subject to remarketing within twelve months	500,000,000
Debt with interest rate periods that expire in the next 12 months	0.75
7.1% senior notes due August 2026 [Member]
Debt
Debt maturing or subject to remarketing within twelve months	$ 223,000,000
Interest rate (as a percent)	7.10%
Canadian Senior Notes [Member]
Debt
Debt maturing or subject to remarketing within twelve months	$ 359,000,000
Interest rate (as a percent)	2.60%	2.60%
Other Debt [Member]
Debt
Debt maturing or subject to remarketing within twelve months	$ 380,000,000
Revolving Credit Facility [Member]
Debt
Maximum capacity	3,500,000,000
Outstanding borrowings under credit facility	0
Letters of credit outstanding	227,000,000
Unused and available credit capacity	$ 2,400,000,000
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	$ 887,000,000