Leases (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018	Dec. 31, 2018
Leases
Operating lease cost	$ 21.1	$ 20.5	$ 41.9	$ 40.4
Cash payments for operating leases (six months ended)			41.4
Right-of-use assets obtained in exchange for lease obligations (six months ended)			$ 28.6
Weighted average remaining lease term - operating leases	5 years 8 months 12 days		5 years 8 months 12 days
Weighted average discount rate - operating leases	4.50%		4.50%
Maturities of operating lease liabilities
2019 (remaining six months)	$ 31.4		$ 31.4
2020	53.7		53.7
2021	41.5		41.5
2022	30.4		30.4
2023	23.3		23.3
Thereafter	55.7		55.7
Total operating lease payments	236.0		236.0
Less: imputed interest	(46.7)		(46.7)
Total operating lease liabilities	$ 189.3		$ 189.3
Maturities of non-cancellable operating leases under ASC 840.
2019					$ 59.5
2020					45.5
2021					32.9
2022					22.7
2023					16.2
Thereafter					40.7
Total operating lease payments					$ 217.5