Goodwill and Other Intangible Assets, Goodwill impairment results (Details) $ in Millions	9 Months Ended	12 Months Ended
Sep. 30, 2018 USD ($) segment	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)
Goodwill and Other Intangible Assets
Number of reportable business segments \| segment	2
Goodwill impairment \| $	$ 0.0	$ 0.0	$ 0.0

Amount of loss from the write-down of an asset representing the future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized.

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