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Debt - Borrowings and Repayments (Detail) $ in Millions, $ in Millions	1 Months Ended		6 Months Ended
	Jun. 30, 2026 USD ($)	Jun. 30, 2026 CAD ($)	Jun. 30, 2026 USD ($)	Jun. 30, 2025 USD ($)	Jun. 30, 2026 CAD ($)	Dec. 31, 2025
Debt
Net proceeds			$ 12,823	$ 9,135
Debt repayments			12,484	$ 9,234
Canadian Senior Notes maturing July 2033
Debt
Debt instrument face amount	$ 493		$ 493		$ 700
Interest rate (as a percent)	3.944%		3.944%		3.944%
Net proceeds	$ 490	$ 696
Canadian Senior Notes [Member]
Debt
Debt instrument face amount					$ 500
Interest rate (as a percent)	2.60%		2.60%		2.60%	2.60%
Commercial Paper Program [Member]
Debt
Commercial paper borrowings			$ 12,300
Commercial paper repayments			12,400
Financing leases and other [Member]
Debt
Non-cash financing lease incurred			97
Debt repayments			$ 98