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Contract Liabilities and Other Disclosures
12 Months Ended
Dec. 31, 2020
Contract Liabilities And Other Disclosures [Abstract]  
Contract Liabilities and Other Disclosures
11. Contract Liabilities and Other Disclosures

The following table summarizes contract related balances:


   Accounts
Receivable
   Unbilled
Accounts
Receivable
   Deferred
Income
   Customer
Prepayments
and Deposits
 
   (in millions) 
At December 31, 2020  $30.4   $8.2   $(22.9)  $(1.6)
At December 31, 2019  $24.5   $15.3   $(27.8)  $(1.9)
At December 31, 2018  $11.5   $11.0   $(32.0)  $(3.6)

Revenue recognized that was included in the deferred income balance at the beginning of the period amounted to $10.3 million and $9.6 million for the years ended December 31, 2020 and 2019, respectively.