Debt (Details) $ in Millions, $ in Millions	3 Months Ended		12 Months Ended
	Mar. 31, 2025 USD ($)	Mar. 31, 2025 CAD ($)	Dec. 31, 2024 USD ($)	Mar. 31, 2025 CAD ($)	Dec. 31, 2024 CAD ($)
Debt Instrument [Line Items]
Commercial paper borrowings			$ 1,102		$ 1,586
5-Year Credit Facility | Revolving Credit Facility
Debt Instrument [Line Items]
Line of credit facility, current borrowing capacity			1,100
2-Year Credit Facility | Revolving Credit Facility
Debt Instrument [Line Items]
Line of credit facility, current borrowing capacity			1,100
Long-term debt			$ 200		$ 288
2.900% 10-year Notes | Senior Notes
Debt Instrument [Line Items]
Repayment of note	$ 642	$ 930
Interest rate	2.90%			2.90%
Note term	10 years	10 years
4.80% 5-year Note
Debt Instrument [Line Items]
Proceeds from issuance of unsecured debt	$ 596	$ 857
4.80% 5-year Note | Unsecured Debt
Debt Instrument [Line Items]
Interest rate	4.80%			4.80%
Note term	5 years	5 years
Debt instrument, face amount	$ 600
5.20% 10-year Note
Debt Instrument [Line Items]
Proceeds from issuance of unsecured debt	$ 593	$ 853
5.20% 10-year Note | Unsecured Debt
Debt Instrument [Line Items]
Interest rate	5.20%			5.20%
Note term	10 years	10 years
Debt instrument, face amount	$ 600
Commercial Paper | Unsecured Debt
Debt Instrument [Line Items]
Maximum borrowing capacity (up to)	1,500
Commercial paper borrowings	$ 786			$ 1,129
Weighted average interest rate	4.60%		4.75%	4.60%	4.75%
Second Amended and Restated Credit Agreement | Revolving Credit Facility
Debt Instrument [Line Items]
Maximum borrowing capacity (up to)	$ 2,200
Line of Credit | 5-Year Credit Facility | Revolving Credit Facility
Debt Instrument [Line Items]
Note term			5 years
Line of Credit | 2-Year Credit Facility | Revolving Credit Facility
Debt Instrument [Line Items]
Note term			2 years
Long-term debt			$ 200
Repayments of long-term debt	200
Term Facility | Unsecured Debt
Debt Instrument [Line Items]
Proceeds from term loan	500
Repayments of term loan	$ 500