Acquisitions Cash Paid for Acquisitions (Details) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018
Cash Paid for Acquisitions [Abstract]
Cost of investment: current-year acquisitions	$ 0.6	$ 12.3
Cost of investment: prior-year acquisitions	15.3	30.6
Less: net cash acquired	0.0	(0.5)
Total cost of investment	15.9	42.4
Operating payments	9.3	18.3
Total cash paid for acquisitions	25.2	60.7
Payments to Acquire Businesses, Net of Cash Acquired	0.6	12.0
Payments for Previous Acquisition	$ 15.3	$ 30.4