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Revenue - Significant Changes in Contract Liabilities (Details) - USD ($)
$ in Millions
12 Months Ended
Dec. 31, 2018
Dec. 31, 2017
Contract With Customer, Asset (Liability) [Roll Forward]    
Beginning balance $ (0.9) $ (0.2)
Payments received / amounts billed 3.8 (2.2)
Costs incurred / revenue recognized 3.6 1.5
Ending balance $ (1.1) $ (0.9)