Benefit Plans (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
Components of net periodic benefit cost
Contributions to qualified and non qualified pension plans	$ 1.1	$ 11.1
Pension Plan [Member]
Components of net periodic benefit cost
Service cost	0.9	0.9
Interest cost	6.2	5.9
Expected return on plan assets	(6.7)	(6.7)
Recognized net actuarial loss	1.4	1.7
Net periodic pension benefit cost	1.8	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	0.1	0.1
Net periodic pension benefit cost	$ 0.2	$ 0.2