Description of the Business and Significant Accounting Policies (Cash and Equivalents, and Restricted Cash and Equivalents) (Details) - USD ($) $ in Millions	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018
Description of the Business and Significant Accounting Policies
Restricted Cash and Cash Equivalents	$ 5.9	$ 5.5	$ 5.9	$ 6.2	$ 5.8	$ 6.2
Restricted Cash and Cash Equivalents, Asset, Statement of Financial Position [Extensible List]	Other Assets, Noncurrent	Other Assets, Noncurrent	Other Assets, Noncurrent	Other Assets, Noncurrent	Other Assets, Noncurrent	Other Assets, Noncurrent