Financial and capital management - Maturity Analysis for Recognized Financial Liabilities (Details) $ in Millions, $ in Millions	12 Months Ended
	Dec. 31, 2024 CAD ($)	Dec. 31, 2024 USD ($)	Dec. 31, 2023 CAD ($)	Dec. 31, 2023 USD ($)
Disclosure of maturity analysis for non-derivative financial liabilities [line items]
Duration of maturity of financial liabilities	5 years
Loan secured by receivables
Disclosure of maturity analysis for non-derivative financial liabilities [line items]
Current borrowings	$ 1,600	$ 1,112	$ 1,588	$ 1,200
Trade receivables
Disclosure of maturity analysis for non-derivative financial liabilities [line items]
Total debt, excluding lease liabilities	36,862		34,527
Trade receivables \| Lease liabilities
Disclosure of maturity analysis for non-derivative financial liabilities [line items]
Total debt, excluding lease liabilities	4,591		4,857
Trade receivables \| Notes payable
Disclosure of maturity analysis for non-derivative financial liabilities [line items]
Current borrowings	2,203		207
Trade receivables \| Loan secured by receivables
Disclosure of maturity analysis for non-derivative financial liabilities [line items]
Current borrowings	1,600		$ 1,588
Liquidity risk
Disclosure of maturity analysis for non-derivative financial liabilities [line items]
Interest payable on long-term debt, notes payable and loan secured by receivables	18,206
Net receipts on cross currency interest rate swaps and interest rate swaps	(1,566)
Total	58,227
Liquidity risk \| 2025
Disclosure of maturity analysis for non-derivative financial liabilities [line items]
Interest payable on long-term debt, notes payable and loan secured by receivables	1,491
Net receipts on cross currency interest rate swaps and interest rate swaps	(64)
Total	9,257
Liquidity risk \| 2026
Disclosure of maturity analysis for non-derivative financial liabilities [line items]
Interest payable on long-term debt, notes payable and loan secured by receivables	1,255
Net receipts on cross currency interest rate swaps and interest rate swaps	(61)
Total	4,173
Liquidity risk \| 2027
Disclosure of maturity analysis for non-derivative financial liabilities [line items]
Interest payable on long-term debt, notes payable and loan secured by receivables	1,213
Net receipts on cross currency interest rate swaps and interest rate swaps	(40)
Total	3,437
Liquidity risk \| 2028
Disclosure of maturity analysis for non-derivative financial liabilities [line items]
Interest payable on long-term debt, notes payable and loan secured by receivables	1,155
Net receipts on cross currency interest rate swaps and interest rate swaps	(40)
Total	3,646
Liquidity risk \| 2029
Disclosure of maturity analysis for non-derivative financial liabilities [line items]
Interest payable on long-term debt, notes payable and loan secured by receivables	1,055
Net receipts on cross currency interest rate swaps and interest rate swaps	(39)
Total	2,838
Liquidity risk \| Thereafter
Disclosure of maturity analysis for non-derivative financial liabilities [line items]
Interest payable on long-term debt, notes payable and loan secured by receivables	12,037
Net receipts on cross currency interest rate swaps and interest rate swaps	(1,322)
Total	34,876
Liquidity risk \| Trade receivables \| Total debt, excluding lease liabilities
Disclosure of maturity analysis for non-derivative financial liabilities [line items]
Total debt, excluding lease liabilities	32,271
Liquidity risk \| Trade receivables \| Total debt, excluding lease liabilities \| 2025
Disclosure of maturity analysis for non-derivative financial liabilities [line items]
Total debt, excluding lease liabilities	2,769
Liquidity risk \| Trade receivables \| Total debt, excluding lease liabilities \| 2026
Disclosure of maturity analysis for non-derivative financial liabilities [line items]
Total debt, excluding lease liabilities	1,988
Liquidity risk \| Trade receivables \| Total debt, excluding lease liabilities \| 2027
Disclosure of maturity analysis for non-derivative financial liabilities [line items]
Total debt, excluding lease liabilities	1,771
Liquidity risk \| Trade receivables \| Total debt, excluding lease liabilities \| 2028
Disclosure of maturity analysis for non-derivative financial liabilities [line items]
Total debt, excluding lease liabilities	2,139
Liquidity risk \| Trade receivables \| Total debt, excluding lease liabilities \| 2029
Disclosure of maturity analysis for non-derivative financial liabilities [line items]
Total debt, excluding lease liabilities	1,490
Liquidity risk \| Trade receivables \| Total debt, excluding lease liabilities \| Thereafter
Disclosure of maturity analysis for non-derivative financial liabilities [line items]
Total debt, excluding lease liabilities	22,114
Liquidity risk \| Trade receivables \| Lease liabilities
Disclosure of maturity analysis for non-derivative financial liabilities [line items]
Current borrowings	5,513
Interest expense on debt instruments issued	922
Liquidity risk \| Trade receivables \| Lease liabilities \| 2025
Disclosure of maturity analysis for non-derivative financial liabilities [line items]
Current borrowings	1,258
Liquidity risk \| Trade receivables \| Lease liabilities \| 2026
Disclosure of maturity analysis for non-derivative financial liabilities [line items]
Current borrowings	991
Liquidity risk \| Trade receivables \| Lease liabilities \| 2027
Disclosure of maturity analysis for non-derivative financial liabilities [line items]
Current borrowings	493
Liquidity risk \| Trade receivables \| Lease liabilities \| 2028
Disclosure of maturity analysis for non-derivative financial liabilities [line items]
Current borrowings	392
Liquidity risk \| Trade receivables \| Lease liabilities \| 2029
Disclosure of maturity analysis for non-derivative financial liabilities [line items]
Current borrowings	332
Liquidity risk \| Trade receivables \| Lease liabilities \| Thereafter
Disclosure of maturity analysis for non-derivative financial liabilities [line items]
Current borrowings	2,047
Liquidity risk \| Trade receivables \| Notes payable
Disclosure of maturity analysis for non-derivative financial liabilities [line items]
Current borrowings	2,203
Liquidity risk \| Trade receivables \| Notes payable \| 2025
Disclosure of maturity analysis for non-derivative financial liabilities [line items]
Current borrowings	2,203
Liquidity risk \| Trade receivables \| Notes payable \| 2026
Disclosure of maturity analysis for non-derivative financial liabilities [line items]
Current borrowings	0
Liquidity risk \| Trade receivables \| Notes payable \| 2027
Disclosure of maturity analysis for non-derivative financial liabilities [line items]
Current borrowings	0
Liquidity risk \| Trade receivables \| Notes payable \| 2028
Disclosure of maturity analysis for non-derivative financial liabilities [line items]
Current borrowings	0
Liquidity risk \| Trade receivables \| Notes payable \| 2029
Disclosure of maturity analysis for non-derivative financial liabilities [line items]
Current borrowings	0
Liquidity risk \| Trade receivables \| Notes payable \| Thereafter
Disclosure of maturity analysis for non-derivative financial liabilities [line items]
Current borrowings	0
Liquidity risk \| Trade receivables \| Loan secured by receivables
Disclosure of maturity analysis for non-derivative financial liabilities [line items]
Current borrowings	1,600
Liquidity risk \| Trade receivables \| Loan secured by receivables \| 2025
Disclosure of maturity analysis for non-derivative financial liabilities [line items]
Current borrowings	1,600
Liquidity risk \| Trade receivables \| Loan secured by receivables \| 2026
Disclosure of maturity analysis for non-derivative financial liabilities [line items]
Current borrowings	0
Liquidity risk \| Trade receivables \| Loan secured by receivables \| 2027
Disclosure of maturity analysis for non-derivative financial liabilities [line items]
Current borrowings	0
Liquidity risk \| Trade receivables \| Loan secured by receivables \| 2028
Disclosure of maturity analysis for non-derivative financial liabilities [line items]
Current borrowings	0
Liquidity risk \| Trade receivables \| Loan secured by receivables \| 2029
Disclosure of maturity analysis for non-derivative financial liabilities [line items]
Current borrowings	0
Liquidity risk \| Trade receivables \| Loan secured by receivables \| Thereafter
Disclosure of maturity analysis for non-derivative financial liabilities [line items]
Current borrowings	$ 0