Income Taxes (Summary Of Tax Years By Jurisdiction) (Details)	12 Months Ended
	Dec. 31, 2017
Maximum [Member] | Canada [Member] | Domestic Tax Authority [Member]
Income Tax Examination [Line Items]
Taxation Year	2017
Maximum [Member] | Canada [Member] | Provincial/State [Member]
Income Tax Examination [Line Items]
Taxation Year	2017
Maximum [Member] | United States [Member] | Internal Revenue Service (IRS) [Member]
Income Tax Examination [Line Items]
Taxation Year	2017
Maximum [Member] | United States [Member] | Provincial/State [Member]
Income Tax Examination [Line Items]
Taxation Year	2017
Maximum [Member] | Other Countries [Member] | Other Taxing Authority [Member]
Income Tax Examination [Line Items]
Taxation Year	2017
Minimum [Member] | Canada [Member] | Domestic Tax Authority [Member]
Income Tax Examination [Line Items]
Taxation Year	2009
Minimum [Member] | Canada [Member] | Provincial/State [Member]
Income Tax Examination [Line Items]
Taxation Year	2009
Minimum [Member] | United States [Member] | Internal Revenue Service (IRS) [Member]
Income Tax Examination [Line Items]
Taxation Year	2014
Minimum [Member] | United States [Member] | Provincial/State [Member]
Income Tax Examination [Line Items]
Taxation Year	2013
Minimum [Member] | Other Countries [Member] | Other Taxing Authority [Member]
Income Tax Examination [Line Items]
Taxation Year	2016