Employee Benefits (Details) - Other Postretirement Benefit Plans, Defined Benefit [Member] - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 1.3	$ 1.6	$ 2.6	$ 3.2
Interest cost	12.8	14.0	25.6	28.0
Expected return on plan assets	(14.8)	(14.1)	(29.6)	(28.2)
Amortization of net pension loss	3.9	3.4	7.8	6.8
Total periodic pension cost	3.2	$ 4.9	6.4	$ 9.8
Expected future benefit payments, remainder of the year	$ 54.1		54.1
Contributions by employer			$ 14.4