Summary of Significant Accounting Policies (Schedule of Cash and Cash Equivalents) (Details) - USD ($) $ in Millions	Jun. 30, 2018	Dec. 31, 2017	Jun. 30, 2017	Dec. 31, 2016
Accounting Policies [Abstract]
Cash and cash equivalents	$ 55.7	$ 8.2	$ 27.2	$ 14.6
Restricted cash and cash equivalents	338.0	255.6	313.9	224.7
Total cash, cash equivalents, restricted cash and restricted cash equivalents	$ 393.7	$ 263.8	$ 341.1	$ 239.3