Debt - Components (Detail) $ in Millions, $ in Millions	Mar. 31, 2023 USD ($)	Mar. 31, 2023 CAD ($)	Dec. 31, 2022 USD ($)	Dec. 31, 2022 CAD ($)
Debt
Debt	$ 15,370		$ 14,984
Debt issuance costs, discounts and other	(91)		(88)
Current portion of long-term debt	336		414
Long-term debt, less current portion	15,034		14,570
Commercial Paper Program [Member]
Debt
Debt	$ 863		$ 1,730
Weighted average interest rate	5.20%	5.20%	4.90%	4.90%
Senior Notes, Aggregate [Member]
Debt
Debt	$ 9,876		$ 8,626
Weighted average interest rate	3.40%	3.40%	3.20%	3.20%
Senior Notes, Aggregate [Member] \| Minimum [Member]
Debt
Interest rate (as a percent)	0.75%	0.75%	0.75%	0.75%
Senior Notes, Aggregate [Member] \| Maximum [Member]
Debt
Interest rate (as a percent)	7.75%	7.75%	7.75%	7.75%
Term Loan maturing May 2024 [Member]
Debt
Debt	$ 1,000		$ 1,000
Effective interest rate (as a percent)	5.60%	5.60%	5.10%	5.10%
Canadian Senior Notes [Member]
Debt
Debt	$ 370	$ 500	$ 369	$ 500
Interest rate (as a percent)	2.60%	2.60%	2.60%	2.60%
Tax Exempt Bonds [Member]
Debt
Debt	$ 2,648		$ 2,648
Weighted average interest rate	2.80%	2.80%	2.70%	2.70%
Tax Exempt Bonds [Member] \| Minimum [Member]
Debt
Interest rate (as a percent)	0.40%	0.40%	0.40%	0.40%
Tax Exempt Bonds [Member] \| Maximum [Member]
Debt
Interest rate (as a percent)	4.40%	4.40%	4.40%	4.40%
Financing leases and other [Member]
Debt
Debt	$ 704		$ 699
Weighted average interest rate	4.70%	4.70%	4.70%	4.70%

Amount of short-term and long-term debt and lease obligation.

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Amount of debt and lease obligation, classified as current.

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- Definition

Effective interest rate for the funds borrowed under the debt agreement considering interest compounding and original issue discount or premium.

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Contractual interest rate for funds borrowed, under the debt agreement.

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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Amount of unamortized debt discount (premium) and debt issuance costs.

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- Definition

Weighted average interest rate of debt outstanding.

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- Definition

Amount of long-term debt and lease obligation, classified as noncurrent.

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