Lease Disclosures Components of Lease Cost (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Finance lease cost:
Amortization of right-of-use assets	$ 1.3	$ 1.3	$ 2.5	$ 2.6
Interest on lease liabilities	1.6	2.0	3.4	4.1
Operating lease cost	26.6	26.8	53.1	53.2
Variable lease cost	(0.1)	0.6	0.3	1.3
Short-term lease cost	0.0	0.0	0.0	0.0
Sublease income	(21.5)	(27.3)	(48.1)	(55.4)
Lease cost	$ 7.9	$ 3.4	$ 11.2	$ 5.8