Restricted Securities Available For Sale (Restricted Securities Available For Sale) (Details) - USD ($) $ in Millions		Dec. 31, 2020	Dec. 31, 2019
Debt Securities, Available-for-sale [Line Items]
Cost		$ 64.1	$ 58.3
Gross Unrealized Gains		2.0	1.0
Gross Unrealized Losses		0.0	0.0
Total restricted securities available for sale	[1]	66.1	59.3
Corporate bonds [Member]
Debt Securities, Available-for-sale [Line Items]
Cost		31.3	25.3
Gross Unrealized Gains		1.1	0.5
Gross Unrealized Losses		0.0	0.0
Total restricted securities available for sale		32.4	25.8
US Government and agency securities [Member]
Debt Securities, Available-for-sale [Line Items]
Cost		19.7	21.3
Gross Unrealized Gains		0.7	0.4
Gross Unrealized Losses		0.0	0.0
Total restricted securities available for sale		20.4	21.7
Asset-backed Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Cost		12.7	11.2
Gross Unrealized Gains		0.2	0.1
Gross Unrealized Losses		0.0	0.0
Total restricted securities available for sale		12.9	11.3
Mortgage-backed securities [Member]
Debt Securities, Available-for-sale [Line Items]
Cost		0.4	0.5
Gross Unrealized Gains		0.0	0.0
Gross Unrealized Losses		0.0	0.0
Total restricted securities available for sale		$ 0.4	$ 0.5

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