Summary of Significant Accounting Policies (Schedule of Cash and Cash Equivalents) (Details) - USD ($) $ in Millions	Sep. 30, 2018	Dec. 31, 2017	Sep. 30, 2017	Dec. 31, 2016
Accounting Policies [Abstract]
Cash and cash equivalents	$ 195.7	$ 8.2	$ 4.9	$ 14.6
Restricted cash and cash equivalents	347.6	255.6	273.6	224.7
Total cash, cash equivalents, restricted cash and restricted cash equivalents	$ 543.3	$ 263.8	$ 278.5	$ 239.3