Summary of Significant Accounting Policies (Details) - USD ($) $ in Millions	Sep. 30, 2020	Dec. 31, 2019	Sep. 30, 2019	Dec. 31, 2018
Cash, Cash Equivalents and Restricted Cash:
Cash and cash equivalents	$ 1,032.2	$ 334.7
Restricted cash	98.9	75.3
Total cash, cash equivalents and restricted cash shown in the Unaudited Condensed Statements of Consolidated Cash Flows	$ 1,131.1	$ 410.0	$ 1,207.8	$ 410.1