Restricted Securities Available For Sale (Schedule Of Cost And Estimated Fair Values Of Debt Securities By Contractual Maturity) (Details) - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2015
Investments, Debt and Equity Securities [Abstract]
Within one year, cost	$ 1.6	$ 2.6
Over one year to five years, cost	39.3	42.5
Over five years to ten years, cost	2.2	0.5
Over ten years, cost	2.4	2.9
Total restricted securities available for sale, cost	45.5	48.5
Within one year, estimated fair value	1.6	2.6
Over one year to five years, estimated fair value	39.1	42.4
Over five years to ten years, estimated fair value	2.2	0.5
Over ten years, fair value	2.4	2.8
Total restricted securities available for sale, estimated fair value	$ 45.3	$ 48.3