Debt (Schedule Of Average Commercial Paper Balances Outstanding And Weighted Average Interest Rates) (Details) - Commercial Paper [Member] - USD ($) $ in Millions	1 Months Ended
	Dec. 31, 2017	Nov. 30, 2017	Oct. 31, 2017	Sep. 30, 2017	Aug. 31, 2017	Jul. 31, 2017	Jun. 30, 2017	May 31, 2017	Apr. 30, 2017	Mar. 31, 2017	Feb. 28, 2017	Jan. 31, 2017
Short-term Debt [Line Items]
Average Balance	$ 48.7	$ 46.0	$ 48.4	$ 45.7	$ 41.5	$ 41.1	$ 40.2	$ 42.4	$ 44.4	$ 60.9	$ 63.0	$ 65.0
Weighted Average Interest Rate	1.67%	1.39%	1.39%	1.40%	1.40%	1.40%	1.29%	1.14%	1.14%	1.04%	0.92%	0.94%