Revenue Recognition (Customer Accounts Receivable) (Details) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2020	Dec. 31, 2019
Revenue from Contract with Customer [Abstract]
Customer Accounts Receivable, Billed (Less Reserve)	$ 291.0	$ 466.6
Customer Accounts Receivable, Unbilled (Less Reserve)	178.8	$ 346.6
Increase (Decrease) in Customer Accounts Receivable, Billed (Less Reserve)	(175.6)
Increase (Decrease) in Customer Accounts Receivable, Unbilled (Less Reserve)	$ (167.8)