Restricted Securities Available For Sale (Schedule Of Restricted Securities Available For Sale By Aging Category) (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Schedule of Available-for-sale Securities [Line Items]
Estimated Fair Value, Less than 12 Months	$ 28.2	$ 33.4
Gross Unrealized Losses, Less than 12 Months	(0.2)	(0.3)
Estimated Fair Value,12 Months or More	12.0	0.0
Gross Unrealized Losses, 12 Months or More	(0.1)	0.0
Total Estimated Fair Value	40.2	33.4
Total Gross Unrealized Losses	(0.3)	(0.3)
US Government and agency securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Estimated Fair Value, Less than 12 Months	11.0	16.4
Gross Unrealized Losses, Less than 12 Months	(0.1)	(0.1)
Estimated Fair Value,12 Months or More	7.9	0.0
Gross Unrealized Losses, 12 Months or More	(0.1)	0.0
Total Estimated Fair Value	18.9	16.4
Total Gross Unrealized Losses	(0.2)	(0.1)
Corporate bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Estimated Fair Value, Less than 12 Months	11.1	11.8
Gross Unrealized Losses, Less than 12 Months	(0.1)	(0.2)
Estimated Fair Value,12 Months or More	1.9	0.0
Gross Unrealized Losses, 12 Months or More	0.0	0.0
Total Estimated Fair Value	13.0	11.8
Total Gross Unrealized Losses	(0.1)	(0.2)
Asset-backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Estimated Fair Value, Less than 12 Months	4.9	2.8
Gross Unrealized Losses, Less than 12 Months	0.0	0.0
Estimated Fair Value,12 Months or More	1.0	0.0
Gross Unrealized Losses, 12 Months or More	0.0	0.0
Total Estimated Fair Value	5.9	2.8
Total Gross Unrealized Losses	0.0	0.0
Mortgage-backed securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Estimated Fair Value, Less than 12 Months	1.2	2.4
Gross Unrealized Losses, Less than 12 Months	0.0	0.0
Estimated Fair Value,12 Months or More	1.2	0.0
Gross Unrealized Losses, 12 Months or More	0.0	0.0
Total Estimated Fair Value	2.4	2.4
Total Gross Unrealized Losses	$ 0.0	$ 0.0