Employee Benefits Schedule of Net Periodic Benefit Cost and Other Comprehensive Income for Pension and Other Postretirement Benefit Plans (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Components of net periodic benefit cost
Curtailment (gain) loss	$ (1.2)	$ (0.1)
Pension Plan and SERP [Member]
Components of net periodic benefit cost
Service cost	0.3	0.8	$ 0.8
Interest cost	4.8	4.6	4.7
Expected return on plan assets	(5.9)	(5.8)	(5.4)
Curtailment (gain) loss	2.0	0.3	0.7
Settlements	0.0	0.0	0.2
Amortization of prior service costs	0.4	0.8	1.0
Amortization of actuarial loss	0.5	0.8	0.5
Periodic expense	2.1	1.5	2.5
Components recognized in accumulated other comprehensive income
Current period prior service cost	0.0	0.0	(0.7)
Current period actuarial (gain) loss	(2.4)	5.6	(7.5)
Amortization of prior service cost	(0.4)	(0.8)	(1.0)
Amortization of actuarial gain (loss)	(0.5)	(0.8)	(0.5)
Loss on curtailment in current period	(0.8)	(0.1)	(0.3)
Settlements	0.0	0.0	(0.2)
Total amount recognized in accumulated other comprehensive income	(4.1)	3.9	(10.2)
Medical Plan [Member]
Components of net periodic benefit cost
Service cost	0.0	0.0	0.0
Interest cost	0.1	0.1	0.1
Expected return on plan assets	0.0	0.0	0.0
Curtailment (gain) loss	(0.8)	(0.2)	0.0
Settlements	0.0	0.0	0.0
Amortization of prior service costs	0.0	(0.3)	(0.3)
Amortization of actuarial loss	0.0	0.0	(0.1)
Periodic expense	(0.7)	(0.4)	(0.3)
Components recognized in accumulated other comprehensive income
Current period prior service cost	0.0	0.2	(2.5)
Current period actuarial (gain) loss	0.9	(0.1)	(0.1)
Amortization of prior service cost	0.8	0.3	0.3
Amortization of actuarial gain (loss)	0.0	0.0	0.1
Loss on curtailment in current period	0.0	0.0	0.0
Settlements	0.0	0.0	0.0
Total amount recognized in accumulated other comprehensive income	$ 1.7	$ 0.4	$ (2.2)