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Revenue and Contracts with Customers Accounts Receivable (Schedule of Accounts Receivable) (Details) - USD ($)
$ in Millions
Dec. 31, 2020
Dec. 31, 2019
Accounts, Notes, Loans and Financing Receivable [Line Items]    
Billed Contracts Receivable $ 23.0 $ 13.2
Unbilled Receivables, Current 6.6 7.9
Accounts receivable, net $ 29.6 $ 21.1