Employee Benefits (Details) - Other Postretirement Benefit Plans, Defined Benefit [Member] - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 0.1	$ 1.3
Interest cost	10.9	12.8
Expected return on plan assets	(15.1)	(14.8)
Amortization of prior service credit	(0.1)	0.0
Amortization of net pension loss	3.7	3.9
Total periodic pension cost	(0.5)	$ 3.2
Expected future benefit payments, remainder of the year	15.4
Contributions by employer	$ 0.3