Goodwill and Other Intangible Assets (Goodwill and Intangible Assets Rollforward) (Details) - USD ($) $ in Millions		12 Months Ended
	Oct. 05, 2017	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Goodwill [Roll Forward]
Beginning balance		$ 25.9	$ 18.6
Acquisitions of businesses and asset groups (2)			7.6
Wobi write-off			(0.3)
Ending balance		25.9	25.9	$ 18.6
Finite-lived Intangible Assets [Roll Forward]
Beginning balance		19.3
Amortization, including foreign currency translation		(10.7)	(10.5)	(8.4)
Ending balance		36.2	19.3
Payments to acquire businesses and interest in affiliates		27.6	13.4	2.6
Other intangible assets
Finite-lived Intangible Assets [Roll Forward]
Beginning balance		19.3	26.9
Acquisitions of businesses and asset groups (2)		27.6	5.0
Wobi write-off			(2.5)
Amortization, including foreign currency translation		(10.7)	(10.5)
Ending balance		$ 36.2	19.3	26.9
Star & Shield LLC | Other intangible assets
Finite-lived Intangible Assets [Roll Forward]
Add: Star & Shield amounts held for sale at beginning of the period			$ 0.4
Less: Star & Shield amounts held for sale at end of the period				$ 0.4
Healthplans.com
Finite-lived Intangible Assets [Roll Forward]
Payments to acquire businesses and interest in affiliates	$ 28.0