Benefit Plans (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Defined Benefit Plan Disclosure [Line Items]
Document Period End Date	Mar. 31, 2017
Components of net periodic benefit cost
Contributions to qualified and non qualified pension plans	$ 6.9	$ 1.1
Pension Plan [Member]
Components of net periodic benefit cost
Service cost	3.6	0.9
Interest cost	7.9	6.2
Expected return on plan assets	(8.6)	(6.7)
Recognized net actuarial loss	1.4	1.4
Net periodic pension benefit cost	4.3	1.8
Other Benefits [Member]
Components of net periodic benefit cost
Service cost	0.0	0.0
Interest cost	0.1	0.1
Expected return on plan assets	0.0	0.0
Recognized net actuarial loss	0.0	0.1
Net periodic pension benefit cost	$ 0.1	$ 0.2