Leases - Statement of Comprehensive Income (Details) $ in Millions	12 Months Ended
	Dec. 31, 2019 USD ($)
Components of lease cost:
Operating lease cost	$ 33.7
Amortization of right-of-use asset	1.1
Total finance lease cost	1.1
Sublease income	7.3
Impairment loss	4.7
UK
Components of lease cost:
Impairment loss	4.7
U.S.
Components of lease cost:
Impairment loss	$ 0.7