Other Compensation Liabilities (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Business Acquisition [Line Items]
Share-based payments liability	$ 221.8	$ 386.1
Profit interests compensation liability	94.8	171.4
Voluntary deferral plan liability	88.3	91.7
Total other compensation liabilities	404.9	649.2
Profit interests compensation expense including discontinued operations	(64.7)	(7.5)	$ 41.5
Redemption of profit sharing interests for cash	12.0	16.1	$ 5.7
Landmark
Business Acquisition [Line Items]
Share-based compensation liability including contingent consideration	$ 188.6	$ 350.6