Compensation Plans (Schedule Of Outstanding Restricted Share Units) (Details) - Restricted Share Units [Member] - shares shares in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Canadian Dollar [Member]
Unvested and Outstanding, Beginning of Year	10,998	8,114
Granted	2,411	7,209
Units, in Lieu of Dividends	60	82
Vested and Released	(2,088)	(2,840)
Forfeited	(352)	(1,567)
Unvested and Outstanding, End of Year	11,029	10,998
United States Of America Dollars [Member]
Unvested and Outstanding, Beginning of Year	10,418	5,909
Granted	2,434	7,826
Units, in Lieu of Dividends	59	80
Vested and Released	(1,268)	(1,446)
Forfeited	(1,109)	(1,951)
Unvested and Outstanding, End of Year	10,534	10,418