Employee Benefits Tables (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Other Postretirement Benefits Plan
Defined Benefit Plan Disclosure
Defined Contribution Plan, Cost	$ 3.9	$ 4.3
Deferred Compensation Arrangement with Individual, Compensation Expense	0.7	0.1
Multiemployer Plan, Contributions by Employer	1.2	1.2
Total other employee benefit plans	7.5	7.1
Postretirement Health Coverage | Salaried VEBA
Defined Benefit Plan Disclosure
Total net periodic postretirement benefit cost relating to Salaried VEBA	1.7	1.5
Salaried VEBA:
Interest cost	0.8	0.7
Expected return on plan assets	(0.6)	(0.7)
Amortization of prior service cost	1.4	1.3
Amortization of net actuarial loss	$ 0.1	$ 0.2