Represents the quantification of the effect of adopting the new accounting standard or change in accounting principle expected by the entity to have a significant effect on the entity's financial statements.

No definition available.

Name:	us-gaap_NewAccountingPronouncementOrChangeInAccountingPrincipleEffectOfAdoptionQuantification
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

Accounting Changes Accounting Changes - Narrative (Details) - Accounting Standards Update 2017-07 [Member] - CAD CAD in Millions	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016	Dec. 31, 2017	Dec. 31, 2016
Change in Accounting Estimate [Line Items]
New Accounting Pronouncement or Change in Accounting Principle, Effect of Adoption, Quantification	CAD 68	CAD 41	CAD 203	CAD 127		CAD 167
Scenario, Forecast [Member]
Change in Accounting Estimate [Line Items]
New Accounting Pronouncement or Change in Accounting Principle, Effect of Adoption, Quantification					CAD 272