Restructuring and other - Restructuring Reserve Roll Forward (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Restructuring Reserve [Roll Forward]
Accrual additions	$ 27.8	$ 7.8	$ 1.1	$ 9.2	$ 36.3	$ 13.8	$ 4.2	$ 2.7	$ 45.9	$ 57.0	$ 21.9
Q4 2016 Plan
Restructuring Reserve [Roll Forward]
Beginning balance				$ 16.4				$ 0.0	16.4	0.0
Accrual additions									2.2	22.4
Cash payments									(18.6)	(6.0)
Ending balance	$ 0.0				$ 16.4				$ 0.0	$ 16.4	$ 0.0