Long term debt and interest expense (Details) $ in Millions, $ in Millions	Dec. 31, 2018 CAD ($)	Dec. 31, 2018 USD ($)	Dec. 31, 2017 CAD ($)	Dec. 31, 2017 USD ($)
Long-term debt and interest expenses
Debt issuance costs		$ (41)		$ (52)
Obligations under finance leases		13		19
Total long-term debt		3,047		2,961
Current portion		(17)		(18)
Total		3,030		2,943
Revolving loan payable
Long-term debt and interest expenses
Long-term debt		595		454
Operating loan payable
Long-term debt and interest expenses
Long-term debt	$ 0		$ 51	40
Term Loan A
Long-term debt and interest expenses
Long-term debt		500		500
Term Loan B
Long-term debt and interest expenses
Long-term debt		$ 1,980		$ 2,000