Leases - Cost and Supplemental Information (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Dec. 31, 2019	Jan. 01, 2019
Leases [Abstract]
Operating lease cost	$ 16.7	$ 15.3
Variable lease cost	3.1	2.3
Finance lease cost	0.1	0.0
Sublease income	(0.5)	(0.4)
Net lease cost	19.4	17.2
Lease ROU assets:
Operating leases	275.9		$ 276.6	$ 248.5
Finance leases	2.5		2.6
Lease liabilities:
Operating leases	307.5		307.9	$ 268.8
Total lease liabilities	$ 5.2		$ 5.3
Weighted-average discount rate:
Operating leases	3.12%		3.13%
Finance leases	2.58%		2.58%
Weighted-average remaining lease term (in years):
Operating leases	7 years 9 months 18 days		7 years 8 months 12 days
Finance leases	11 years 10 months 24 days		12 years 2 months 12 days
Cash payments included in the measurement of lease liabilities:
Reported in operating cash from operating leases	$ 17.1	15.4
Reported in financing cash from finance leases	0.1	0.0
ROU assets obtained in exchange for lessee:
Operating lease liabilities	14.3	10.3
Finance lease liabilities	$ 0.0	$ 0.0