Other Operating Credits and Charges, Net Other Operating Charges, Severance (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Restructuring Cost and Reserve [Line Items]
Beginning balance at December 31,	$ 1.7	$ 0.2	$ 0.2
Severance costs accrued to expense during year	0.3	3.7	0.5
Accrued to other operating charges and credits	10.3	0.0	0.0
Payments	(6.8)	(2.2)	(0.5)
Ending balance	$ 5.5	$ 1.7	$ 0.2