Available For Sale Securities (Restricted Securities Available For Sale) (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Restricted Cash and Cash Equivalents Items [Line Items]
Cost	$ 46.3	$ 0.8
Gross Unrealized Losses	(0.2)
Total restricted securities available for sale	46.1	0.8
Commercial Paper [Member]
Restricted Cash and Cash Equivalents Items [Line Items]
Cost	18.9
Gross Unrealized Losses	(0.1)
Total restricted securities available for sale	18.8
Certificates of Deposit [Member]
Restricted Cash and Cash Equivalents Items [Line Items]
Cost	3.3
Total restricted securities available for sale	3.3
US Government And Agency Securities [Member]
Restricted Cash and Cash Equivalents Items [Line Items]
Cost	20.6
Gross Unrealized Losses	(0.1)
Total restricted securities available for sale	20.5
Foreign Government Bonds [Member]
Restricted Cash and Cash Equivalents Items [Line Items]
Cost	0.2
Total restricted securities available for sale	0.2
Corporate Bonds [Member]
Restricted Cash and Cash Equivalents Items [Line Items]
Cost	3.3	0.8
Total restricted securities available for sale	$ 3.3	$ 0.8