Summary of Significant Accounting Policies (Schedule of Cash and Cash Equivalents) (Details) - USD ($) $ in Millions	Mar. 31, 2018	Dec. 31, 2017	Mar. 31, 2017	Dec. 31, 2016
Accounting Policies [Abstract]
Cash and cash equivalents	$ 11.5	$ 8.2	$ 11.1	$ 14.6
Restricted cash and cash equivalents	368.5	255.6	316.7	224.7
Total cash, cash equivalents, restricted cash and restricted cash equivalents	$ 380.0	$ 263.8	$ 327.8	$ 239.3