Retirement Plans (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016	Dec. 31, 2016
Net Periodic Benefit Cost
Service cost			$ 7.5		$ 8.0
Defined Benefit Pension Plans
Net Periodic Benefit Cost
Service cost	$ 2.7	$ 1.3	7.5	$ 4.7
Interest cost	2.9	2.8	8.4	8.8
Expected return on assets	(2.8)	(2.8)	(8.0)	(8.7)
Curtailment and settlement gain	0.0	(6.8)	0.0	(6.8)
Other	0.1	0.4	1.4	1.0
Total benefit cost	2.9	(5.1)	9.3	(1.0)
Contributions to pension plans	2.0		7.2
Estimated employer contribution to pension plans during current fiscal year			9.6
Retiree Health Care Plan
Net Periodic Benefit Cost
Interest cost	0.1	0.1	0.4	0.5
Net loss	0.1	0.0	0.1	0.0
Prior service credit	(0.3)	(0.2)	(0.6)	(0.6)
Total benefit cost	(0.1)	$ (0.1)	(0.1)	$ (0.1)
Contributions to retiree health care plan	$ 0.3		$ 0.8