Restricted Securities Available for Sale (Schedule of Cost and Estimated Fair Values of Debt Securities by Contractual Maturity) (Details) - USD ($) $ in Millions	Sep. 30, 2016	Dec. 31, 2015
Restricted Cash and Cash Equivalents Items [Line Items]
Within one year, cost	$ 2.3	$ 2.6
Within one year, fair value	2.3	2.6
Over one year to five years, cost	41.3	42.5
Over one year to five years, fair value	41.7	42.4
Over five years to ten years, cost	0.5	0.5
Over five years to ten years, fair value	0.5	0.5
Over ten years, cost	2.5	2.9
Over ten years, fair value	2.5	2.8
Total restricted securities available for sale, cost	46.6	48.5
Total restricted securities available for sale	$ 47.0	$ 48.3