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Summary of Significant Accounting Policies, Accounts Receivable (Details) - USD ($)
$ in Millions
12 Months Ended
Dec. 31, 2019
Dec. 31, 2018
Dec. 31, 2017
Accounts Receivable, after Allowance for Credit Loss [Abstract]      
Unbilled contracts receivable $ 586.6 $ 531.4  
Allowance For Doubtful Accounts, Current. [Member]      
SEC Schedule, 12-09, Valuation and Qualifying Accounts Disclosure [Line Items]      
Allowance at beginning of the year 52.0 51.3 $ 37.1
Charged to income 30.8 18.8 26.3
Write-off of uncollectible receivables (13.8) (13.9) (14.2)
Impact of exchange rate movements and other (0.9) (4.2) 2.1
Allowance at end of the year $ 68.1 $ 52.0 $ 51.3