Acquisitions Cash Paid for Acquisitions (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Cash Paid for Acquisitions [Abstract]
Cost of investment: current-year acquisitions	$ 0.0	$ 8.5	$ 0.6
Cost of investment: prior-year acquisitions	28.0	45.9	15.8
Less: net cash acquired	0.0	(2.9)	0.0
Total cost of investment	28.0	51.5	16.4
Operating payments	39.1	2.9	9.3
Total cash paid for acquisitions	67.1	54.4	25.7
Acquisitions, net of cash acquired	0.0	4.9	0.6
Payments for previous acquisition, financing cash flows	$ 28.0	$ 46.6	$ 15.8