Debt (Details) $ in Millions, $ in Millions	3 Months Ended			6 Months Ended
	Jun. 30, 2025 CAD ($)	Mar. 31, 2025 USD ($)	Mar. 31, 2025 CAD ($)	Jun. 30, 2025 USD ($)	Jun. 30, 2025 CAD ($)	Jun. 30, 2025 CAD ($)	Dec. 31, 2024 USD ($)	Dec. 31, 2024 CAD ($)
Debt Instrument [Line Items]
Commercial paper borrowings							$ 1,102	$ 1,586
2.90% 10-year Note | Senior Notes
Debt Instrument [Line Items]
Repayment of note				$ 642	$ 930
Interest rate				2.90%		2.90%
Note term				10 years	10 years
4.00% 7-year Note
Debt Instrument [Line Items]
Proceeds from issuance of unsecured debt	$ 498
4.00% 7-year Note | Unsecured Debt
Debt Instrument [Line Items]
Debt instrument, face amount						$ 500
Interest rate				4.00%		4.00%
Note term	7 years
4.40% 10.5-year Note
Debt Instrument [Line Items]
Proceeds from issuance of unsecured debt	$ 598
4.40% 10.5-year Note | Unsecured Debt
Debt Instrument [Line Items]
Debt instrument, face amount						$ 600
Interest rate				4.40%		4.40%
Note term	10 years 6 months
4.80% 30-year Note
Debt Instrument [Line Items]
Proceeds from issuance of unsecured debt	$ 296
4.80% 30-year Note | Unsecured Debt
Debt Instrument [Line Items]
Debt instrument, face amount						$ 300
Interest rate				4.80%		4.80%
Note term	30 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]
Debt instrument, face amount				$ 600
Interest rate				4.80%		4.80%
Note term				5 years	5 years
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]
Debt instrument, face amount				$ 600
Interest rate				5.20%		5.20%
Note term				10 years	10 years
Term Facility | Unsecured Debt
Debt Instrument [Line Items]
Proceeds from term loan				$ 500
Repayments of term loan				500
Commercial Paper | Unsecured Debt
Debt Instrument [Line Items]
Maximum borrowing capacity (up to)				1,500
Commercial paper borrowings				$ 250		$ 341
Weighted average interest rate				4.69%		4.69%	4.75%	4.75%
Third Amended and Restated Credit Agreement | Revolving Credit Facility
Debt Instrument [Line Items]
Maximum borrowing capacity (up to)				$ 2,200
5-Year Credit Facility | Line of Credit | Revolving Credit Facility
Debt Instrument [Line Items]
Note term				5 years	5 years
Line of credit facility, current borrowing capacity				$ 1,100
2-Year Credit Facility | Line of Credit | Revolving Credit Facility
Debt Instrument [Line Items]
Note term				2 years	2 years
Line of credit facility, current borrowing capacity				$ 1,100
Long-term debt							$ 200	$ 288
Repayments of long-term debt		$ 200	$ 288