Income Taxes (Summary Of The Tax Years By Jurisdiction That Remain Subject To Examination By Taxing Authorities) (Details)	12 Months Ended
	Dec. 31, 2017
Minimum [Member] | United States Federal [Member]
Tax years open	2012
Minimum [Member] | Canada Federal [Member]
Tax years open	2004
Maximum [Member] | United States Federal [Member]
Tax years open	2017
Maximum [Member] | Canada Federal [Member]
Tax years open	2017
Various U.S. States [Member] | Minimum [Member]
Tax years open	2012
Various U.S. States [Member] | Maximum [Member]
Tax years open	2017
Various Canadian Provinces [Member] | Minimum [Member]
Tax years open	2004
Various Canadian Provinces [Member] | Maximum [Member]
Tax years open	2017