Debt and Derivatives - Components (Detail) $ in Millions, $ in Millions	Dec. 31, 2024 USD ($)	Dec. 31, 2024 CAD ($)	Dec. 31, 2023 USD ($)	Dec. 31, 2023 CAD ($)
Debt
Debt	$ 23,900		$ 16,229
Debt issuance costs, discounts and other	(179)		(123)
Current portion of long-term debt	1,359		334
Long-term debt, less current portion	22,541		15,895
Commercial Paper Program [Member]
Debt
Debt	$ 1,250		$ 860
Weighted average interest rate	4.70%	4.70%	5.60%	5.60%
Senior Notes, Aggregate [Member]
Debt
Debt	$ 18,419		$ 11,376
Weighted average interest rate	4.20%	4.20%	3.70%	3.70%
Senior Notes, Aggregate [Member] | Minimum [Member]
Debt
Interest rate (as a percent)	0.75%	0.75%
Senior Notes, Aggregate [Member] | Maximum [Member]
Debt
Interest rate (as a percent)	7.75%	7.75%
Canadian Senior Notes [Member]
Debt
Debt	$ 348	$ 500	$ 378	$ 500
Interest rate (as a percent)	2.60%	2.60%	2.60%	2.60%
Tax Exempt Bonds [Member]
Debt
Debt	$ 2,873		$ 2,883
Weighted average interest rate	3.70%	3.70%	3.30%	3.30%
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)	4.80%	4.80%
Financing leases and other [Member]
Debt
Debt	$ 1,189		$ 855
Weighted average interest rate	4.90%	4.90%	5.00%	5.00%