Retirement Plans (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016	Dec. 31, 2016
Net Periodic Benefit Cost
Service cost			$ 4.8		$ 8.0
Defined Benefit Pension Plans
Net Periodic Benefit Cost
Service cost	$ 2.4	$ 1.8	4.8	$ 3.4
Interest cost	2.8	3.0	5.5	6.0
Expected return on assets	(2.6)	(3.0)	(5.2)	(5.9)
Other	0.7	0.3	1.3	0.6
Total benefit cost	3.3	2.1	6.4	4.1
Contributions to pension plans	3.8		5.2
Estimated employer contribution to pension plans during current fiscal year			9.0
Retiree Health Care Plan
Net Periodic Benefit Cost
Interest cost	0.2	0.2	0.3	0.4
Prior service credit	(0.2)	(0.2)	(0.3)	(0.4)
Total benefit cost	0.0	$ 0.0	0.0	$ 0.0
Contributions to retiree health care plan	$ 0.2		$ 0.5