Revenue - Impact of ASU Adoption (Details) - USD ($) $ in Millions	3 Months Ended
Mar. 31, 2018	Mar. 31, 2017
Impact of ASU adoption
Income tax expense (benefit)	$ 8.4	$ 9.9
Practical expedient, incremental costs of obtaining a contract	true
ASU No. 2014-09 \| Adjustments
Impact of ASU adoption
Retained earnings	$ 8.2
Income tax expense (benefit)	$ (2.1)

Amount of current income tax expense (benefit) and deferred income tax expense (benefit) pertaining to continuing operations.

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