Restricted Securities Available for Sale (Schedule of Restricted Securities Available for Sale) (Details) - USD ($) $ in Millions	Jun. 30, 2015	Dec. 31, 2014
Restricted Cash and Cash Equivalents Items [Line Items]
Available-for-sale Securities, Amortized Cost Basis	$ 52.1	$ 53.3
Gross Unrealized Gains	0.1	0.1
Gross Unrealized Losses	(0.1)	(0.2)
Estimated Fair Value	52.1	53.2
US Government and Agency Securities [Member]
Restricted Cash and Cash Equivalents Items [Line Items]
Available-for-sale Securities, Amortized Cost Basis	21.0	28.8
Gross Unrealized Gains	0.1	0.1
Gross Unrealized Losses	0.0	(0.1)
Estimated Fair Value	21.1	28.8
Corporate Bond Securities [Member]
Restricted Cash and Cash Equivalents Items [Line Items]
Available-for-sale Securities, Amortized Cost Basis	20.7	19.1
Gross Unrealized Gains	0.0	0.0
Gross Unrealized Losses	(0.1)	(0.1)
Estimated Fair Value	20.6	19.0
Asset-backed Securities [Member]
Restricted Cash and Cash Equivalents Items [Line Items]
Available-for-sale Securities, Amortized Cost Basis	6.2	4.8
Gross Unrealized Gains	0.0	0.0
Gross Unrealized Losses	0.0
Estimated Fair Value	6.2	4.8
Mortgage-backed Securities [Member]
Restricted Cash and Cash Equivalents Items [Line Items]
Available-for-sale Securities, Amortized Cost Basis	4.2	0.6
Gross Unrealized Gains	0.0	0.0
Gross Unrealized Losses	0.0	0.0
Estimated Fair Value	$ 4.2	$ 0.6