Amount after accumulated impairment loss of an asset representing future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized.

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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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Amount of increase (decrease) of an asset representing future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized.

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Business Combinations and Goodwill, Goodwill Rollforward (Details) - USD ($) $ in Millions	3 Months Ended			9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Jun. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Goodwill [Roll Forward]
Goodwill, Gross				$ 37.2
Goodwill, Accumulated Impairment Loss				(18.4)
Goodwill				18.8
Goodwill, Acquired During Period				24.6
Goodwill impairment	$ 0.0	$ 0.0	$ 18.4	0.0	$ 18.4
Goodwill, Increase				24.6
Goodwill, Gross	61.8			61.8
Goodwill, Accumulated Impairment Loss	(18.4)			(18.4)
Goodwill	$ 43.4			$ 43.4