Leases (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2018
Leases
Operating lease cost	$ 20.8	$ 19.8
Operating cash flows from operating leases (three months ended)	(20.2)
Right-of-use assets obtained in exchange for lease obligations (three months ended)	$ 11.7
Weighted average remaining lease term - operating leases	5 years 9 months 18 days
Weighted average discount rate - operating leases	4.60%
Maturities of operating lease liabilities
2019	$ 45.3		$ 59.5
2020	48.8		45.5
2021	36.3		32.9
2022	25.2		22.7
2023	18.2		16.2
Thereafter	45.0		40.7
Total lease payments	218.8		217.5
Less: imputed interest	(32.4)
Total	$ 186.4		$ 217.5