Restricted Securities Available for Sale (Schedule of Restricted Securities Available for Sale by Aging Catagory) (Details) (USD $) In Millions, unless otherwise specified	Mar. 31, 2015	Dec. 31, 2014
Restricted Cash and Cash Equivalents Items [Line Items]
Estimated Fair Value, Less than 12 Months	$ 10.2	$ 28.3
Gross Unrealized Losses, Less than 12 Months	0	(0.1)
Estimated Fair Value, 12 Months or More	3.2	5.2
Gross Unrealized Losses, 12 Months or More	0	(0.1)
Total Estimated Fair Value	13.4	33.5
Total Gross Unrealized Losses	0	(0.2)
Corporate Bond Securities [Member]
Restricted Cash and Cash Equivalents Items [Line Items]
Estimated Fair Value, Less than 12 Months	7.5	15.3
Gross Unrealized Losses, Less than 12 Months	0	(0.1)
Estimated Fair Value, 12 Months or More	0.7	2.7
Gross Unrealized Losses, 12 Months or More	0	0
Total Estimated Fair Value	8.2	18.0
Total Gross Unrealized Losses	0	(0.1)
Asset-backed Securities [Member]
Restricted Cash and Cash Equivalents Items [Line Items]
Estimated Fair Value, Less than 12 Months	0.9	3.7
Estimated Fair Value, 12 Months or More	0	0
Gross Unrealized Losses, 12 Months or More	0	0
Total Estimated Fair Value	0.9	3.7
US Government and Agency Securities [Member]
Restricted Cash and Cash Equivalents Items [Line Items]
Estimated Fair Value, Less than 12 Months	1.8	9.3
Gross Unrealized Losses, Less than 12 Months		0
Estimated Fair Value, 12 Months or More	2.5	2.5
Gross Unrealized Losses, 12 Months or More	0	(0.1)
Total Estimated Fair Value	4.3	11.8
Total Gross Unrealized Losses		$ (0.1)