Summary Of Significant Accounting Policies Summary of Significant Accounting Policies (Schedule of Cash and Cash Equivalents) (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Accounting Policies [Abstract]
Cash and cash equivalents	$ 16.0	$ 187.4	$ 25.7
Restricted cash and cash equivalents	380.2	330.3	303.6
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents	$ 396.2	$ 517.7	$ 329.3	$ 263.8