Benefit Plans, Components of Net Periodic Benefit Costs (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Pension Benefits [Member]
Components of net periodic benefit cost [Abstract]
Service cost	$ 7.9	$ 8.2	$ 10.3
Interest cost	12.6	13.0	15.4
Expected return on plan assets	(18.7)	(18.6)	(19.7)
Amortization of prior service cost	0.0	0.6	0.8
Recognized net actuarial (gain) loss	10.8	10.7	12.1
Settlement/curtailment loss	0.0	0.3	0.0
Net periodic benefit cost	12.6	14.2	18.9
Post-retirement Benefits [Member]
Components of net periodic benefit cost [Abstract]
Service cost	0.3	0.3	0.4
Interest cost	0.3	0.3	0.3
Expected return on plan assets	0.0	0.0	0.0
Amortization of prior service cost	(3.1)	(3.1)	(3.1)
Recognized net actuarial (gain) loss	(0.3)	(0.2)	(0.1)
Settlement/curtailment loss	0.0	0.0	0.0
Net periodic benefit cost	$ (2.8)	$ (2.7)	$ (2.5)