Employee Benefits (Details) - Other Postretirement Benefit Plans, Defined Benefit [Member] - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 1.3	$ 1.6
Interest cost	12.8	14.0
Expected return on plan assets	(14.8)	(14.1)
Amortization of net pension loss	3.9	3.4
Total periodic pension cost	3.2	$ 4.9
Expected future benefit payments, remainder of the year	54.1
Contributions by employer	$ 0.2