Restricted Securities Available For Sale (Restricted Securities Available For Sale) (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Restricted Cash and Cash Equivalents Items [Line Items]
Cost	$ 53.3	$ 53.9
Gross Unrealized Gains	0.1	0
Gross Unrealized Losses	(0.2)	(0.3)
Total restricted securities available for sale	53.2	53.6
Corporate Bond [Member]
Restricted Cash and Cash Equivalents Items [Line Items]
Cost	19.1	3.1
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(0.1)	(0.1)
Total restricted securities available for sale	19.0	3.0
US Government And Agency Securities [Member]
Restricted Cash and Cash Equivalents Items [Line Items]
Cost	28.8	22.3
Gross Unrealized Gains	0.1	0
Gross Unrealized Losses	(0.1)	(0.2)
Total restricted securities available for sale	28.8	22.1
Asset-backed Securities [Member]
Restricted Cash and Cash Equivalents Items [Line Items]
Cost	4.8
Gross Unrealized Gains	0
Gross Unrealized Losses	0
Total restricted securities available for sale	4.8
Collateralized Mortgage Backed Securities [Member]
Restricted Cash and Cash Equivalents Items [Line Items]
Cost	0.6
Gross Unrealized Gains	0
Gross Unrealized Losses	0
Total restricted securities available for sale	0.6
Commercial Paper [Member]
Restricted Cash and Cash Equivalents Items [Line Items]
Cost		23.9
Gross Unrealized Gains		0
Gross Unrealized Losses		0
Total restricted securities available for sale		23.9
Certificates of Deposit [Member]
Restricted Cash and Cash Equivalents Items [Line Items]
Cost		4.6
Gross Unrealized Gains		0
Gross Unrealized Losses		0
Total restricted securities available for sale		$ 4.6