Debt and Derivatives - Components (Detail) $ in Millions, $ in Millions	Sep. 30, 2023 USD ($)	Sep. 30, 2023 CAD ($)	Dec. 31, 2022 USD ($)
Debt
Debt	$ 15,430		$ 14,984
Debt issuance costs, discounts and other	(123)		(88)
Current portion of long-term debt	297		414
Long-term debt, less current portion	15,133		14,570
Commercial Paper Program [Member]
Debt
Debt	$ 490		$ 1,730
Weighted average interest rate	5.50%	5.50%	4.90%
Senior Notes, Aggregate [Member]
Debt
Debt	$ 11,376		$ 8,626
Weighted average interest rate	3.70%	3.70%	3.20%
Senior Notes, Aggregate [Member] | Minimum [Member]
Debt
Interest rate (as a percent)	0.75%	0.75%	0.75%
Senior Notes, Aggregate [Member] | Maximum [Member]
Debt
Interest rate (as a percent)	7.75%	7.75%	7.75%
Term Loan [Member]
Debt
Debt			$ 1,000
Effective interest rate (as a percent)			5.10%
Canadian Senior Notes [Member]
Debt
Debt	$ 368	$ 500	$ 369
Interest rate (as a percent)	2.60%	2.60%	2.60%
Tax Exempt Bonds [Member]
Debt
Debt	$ 2,633		$ 2,648
Weighted average interest rate	2.90%	2.90%	2.70%
Tax Exempt Bonds [Member] | Minimum [Member]
Debt
Interest rate (as a percent)	0.55%	0.55%	0.55%
Tax Exempt Bonds [Member] | Maximum [Member]
Debt
Interest rate (as a percent)	4.40%	4.40%	4.40%
Financing leases and other [Member]
Debt
Debt	$ 686		$ 699
Weighted average interest rate	4.80%	4.80%	4.70%