Restricted Securities Available for Sale (Schedule of Cost and Estimated Fair Values of Debt Securities by Contractual Maturity) (Details) - Cash and Cash Equivalents [Domain] - USD ($) $ in Millions	Jun. 30, 2015	Dec. 31, 2014
Restricted Cash and Cash Equivalents Items [Line Items]
Within one year, cost	$ 5.9	$ 3.8
Within one year, fair value	5.9	3.8
Over one year to five years, cost	42.6	45.1
Over one year to five years, fair value	42.6	45.0
Over five years to ten years, cost	0.7	4.1
Over five years to ten years, fair value	0.7	4.1
Over ten years, cost	2.9	0.3
Over ten years, fair value	2.9	0.3
Total restricted securities available for sale, cost	52.1	53.3
Total restricted securities available for sale	$ 52.1	$ 53.2