Income Taxes - Schedule of deferred tax assets and liabilities (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Deferred tax assets:
Deferred compensation	$ 436.6	$ 519.7
Fixed assets and intangible assets	140.5	192.0
Accrued expenses	139.8	75.9
Deferred revenue	44.6	22.0
Total deferred tax assets	761.5	809.6
Valuation allowance	0.0	(7.0)
Deferred tax assets, net of valuation allowance	761.5	802.6
Deferred tax liabilities:
Other	(42.8)	(11.2)
Net deferred tax assets	$ 718.7	$ 791.4