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Revenue Recognition - Change in Contract Liabilities (Details) - USD ($)
$ in Millions
3 Months Ended
Mar. 31, 2018
Mar. 31, 2017
Revenue from Contract with Customer [Abstract]    
Balance as of January 1 $ 215.8 $ 195.2
Revenue recognized (14.9) (13.0)
Revenue deferred 18.2 20.9
Acquired liabilities 0.1 0.0
Balance as of March 31 $ 219.2 $ 203.1