Lease Disclosures - Components of Lease Cost (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Leases [Abstract]
Amortization of right-of-use assets	$ 5.0	$ 5.3
Interest on lease liabilities	6.6	7.7
Operating lease cost	109.8	106.2
Variable lease cost	0.8	2.7
Short-term lease cost	0.0	0.0
Sublease income	(96.8)	(110.9)
Lease cost	$ 25.4	$ 11.0