Equity - Reconciliation of accumulated other comprehensive income (loss) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Increase (Decrease) in Equity [Roll Forward]
Beginning balance	$ 590.5
Total other comprehensive income (loss), net of tax	65.5	$ (23.1)	$ (77.3)
Distribution of MFS	9.4	(375.8)	65.5
Ending balance	677.5	590.5
Gains and Losses on Cash Flow Hedges
Increase (Decrease) in Equity [Roll Forward]
Beginning balance	(0.3)	(3.8)
Other comprehensive income (loss) before reclassifications	(0.3)	(2.9)
Amounts reclassified from accumulated other comprehensive income (loss)	0.7	4.3
Total other comprehensive income (loss), net of tax	0.4	1.4
Distribution of MFS		2.1
Ending balance	0.1	(0.3)	(3.8)
Pension & Postretirement
Increase (Decrease) in Equity [Roll Forward]
Beginning balance	(51.8)	(82.6)
Other comprehensive income (loss) before reclassifications	7.0	(8.6)
Amounts reclassified from accumulated other comprehensive income (loss)	(0.3)	4.5
Total other comprehensive income (loss), net of tax	6.7	(4.1)
Distribution of MFS		34.9
Ending balance	(45.1)	(51.8)	(82.6)
Foreign Currency Translation
Increase (Decrease) in Equity [Roll Forward]
Beginning balance	(110.8)	(121.4)
Other comprehensive income (loss) before reclassifications	58.4	(20.4)
Total other comprehensive income (loss), net of tax	58.4	(20.4)
Distribution of MFS		31.0
Ending balance	(52.4)	(110.8)	(121.4)
Accumulated Other Comprehensive Loss
Increase (Decrease) in Equity [Roll Forward]
Beginning balance	(162.9)	(207.8)
Other comprehensive income (loss) before reclassifications	65.1	(31.9)
Amounts reclassified from accumulated other comprehensive income (loss)	0.4	8.8
Total other comprehensive income (loss), net of tax	65.5	(23.1)	(77.3)
Distribution of MFS		68.0
Ending balance	$ (97.4)	$ (162.9)	$ (207.8)