Contingencies - Legal Proceedings (Details) - Lac-Megantic Rail Accident [Member] $ in Millions	9 Months Ended
	Sep. 30, 2019 CAD ($) claim
Claimed damages as a result of derailment
Other Commitments [Line Items]
Amount of fund to be distributed	$ 440
Quebec Minister of Sustainable Development, Environment, Wildlife and Parks
Other Commitments [Line Items]
Value of damages sought	95
Attorney General of Quebec
Other Commitments [Line Items]
Value of damages sought	315
Initial value of damages sought	409
Initial Insurer Claimants | Subrogated insurance claim
Other Commitments [Line Items]
Value of damages sought	14
Initial value of damages sought	$ 16
Number of pending claims | claim	8
Additional Insurer Claimants | Subrogated insurance claim
Other Commitments [Line Items]
Value of damages sought	$ 3
Number of pending claims | claim	2
Plaintiffs
Other Commitments [Line Items]
Value of damages sought	$ 5
Number of Plaintiffs | claim	48
Wrongful Death Trustee | Damaged rail cars and lost crude
Other Commitments [Line Items]
Value of damages sought	$ 6
Wrongful Death Trustee | Reimbursement for settlement paid by consignor
Other Commitments [Line Items]
Value of damages sought	110
Wrongful Death Trustee | Reimbursement for settlement paid by consignee
Other Commitments [Line Items]
Value of damages sought	$ 60