Leases - Statement of Comprehensive Income (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Components of lease cost:
Operating lease cost	$ 31.2	$ 33.7
Amortization of right-of-use asset	0.9	1.1
Interest on lease liabilities	0.1
Total finance lease cost	1.0	1.1
Sublease income	3.0	7.3
Impairment of a subleased right-of-use operating asset	$ 1.4	$ 5.4