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Revenue Recognition - Change in Contract Assets (Details) - USD ($)
$ in Millions
6 Months Ended
Jun. 30, 2019
Jun. 30, 2018
Revenue from Contract with Customer [Abstract]    
Balance, beginning $ 44.7 $ 0.0
Adoption of ASC 606 0.0 22.8
Revenue recognized and unbilled 116.3 69.5
Revenue billed (102.9) (49.5)
Balance, ending $ 58.1 $ 42.8