Pension and Postretirement Benefit Costs (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Components of net periodic benefit cost
Income tax benefit	$ (4.5)	$ (65.8)
Pension Plans, Defined Benefit [Member]
Components of net periodic benefit cost
Service cost for benefits earned	0.6	0.6
Interest cost on projected or accumulated postretirement benefit obligation	9.7	10.4
Expected return on plan assets	(11.0)	(11.3)
Amortization of prior service cost and net actuarial loss	6.4	6.2
Net periodic pension or postretirement benefit cost	$ 5.7	5.9
Funding threshhold	80.00%
Estimated contribution in 2016 to pension plan	$ 5.9
Other Postretirement Benefit Plan [Member]
Components of net periodic benefit cost
Service cost for benefits earned	2.3	2.6
Interest cost on projected or accumulated postretirement benefit obligation	8.4	8.8
Amortization of prior service cost and net actuarial loss	3.2	2.4
Net periodic pension or postretirement benefit cost	$ 13.9	$ 13.8