Employee Benefits Schedule of Net Periodic Benefit Cost (Details) - USD ($) $ in Millions		3 Months Ended		6 Months Ended
		Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Medical Plan [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Interest cost		$ 0.1	$ 0.1	$ 0.1	$ 0.1
Amortization of prior service costs	[1]	0.0	0.0	(0.1)	(0.1)
Periodic expense		0.1	0.1	0.0	0.0
Pension Plan and SERP [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Service cost		0.2	0.1	0.4	0.4
Interest cost		1.1	1.2	2.2	2.4
Expected return on plan assets		(1.5)	(1.4)	(2.9)	(2.7)
Amortization of prior service costs	[1]	0.2	0.3	0.4	0.6
Amortization of actuarial losses	[1]	0.3	(0.1)	0.6	0.2
Periodic expense		$ 0.3	$ 0.1	$ 0.7	$ 0.9

[1] Amortization of prior service costs and actuarial losses out of accumulated other comprehensive income are recognized on the Condensed Consolidated Statements of Operations within "Interest and other income (expense)".