Restricted Securities Available For Sale (Schedule Of Cost And Estimated Fair Values Of Debt Securities By Contractual Maturity) (Details) - USD ($) $ in Millions		Dec. 31, 2017	Dec. 31, 2016
Investments, Debt and Equity Securities [Abstract]
Within one year, cost		$ 2.5	$ 1.6
Over one year to five years, cost		40.5	39.3
Over five years to ten years, cost		1.0	2.2
Over ten years, cost		2.4	2.4
Total restricted securities available for sale, cost		46.4	45.5
Within one year, estimated fair value		2.5	1.6
Over one year to five years, estimated fair value		40.2	39.1
Over five years to ten years, estimated fair value		1.0	2.2
Over ten years, fair value		2.4	2.4
Total restricted securities available for sale, estimated fair value	[1]	$ 46.1	$ 45.3

[1] Measured at fair value on a recurring basis.