Description of the Business and Significant Accounting Policies (Cash and Equivalents, and Restricted Cash and Equivalents) (Details) - USD ($) $ in Millions	Jun. 30, 2021	Mar. 31, 2021	Dec. 31, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019
Description of the Business and Significant Accounting Policies
Restricted Cash and Cash Equivalents	$ 5.5	$ 5.5	$ 5.5	$ 5.9	$ 5.5	$ 5.9
Restricted Cash and Cash Equivalents, Asset, Statement of Financial Position [Extensible List]	Other asset	Other asset	Other asset	Other asset		Other asset