Statements of Consolidated Comprehensive Income (Unaudited) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Statement of Comprehensive Income [Abstract]
Net income	$ 21.7	$ 19.9	$ 68.1	$ 60.6
Other Comprehensive Income (Loss), Net of Tax
Defined benefit pension plan and Salaried VEBA	1.1	0.8	3.5	2.5
Available for sale securities	(0.2)	0.3	(0.5)	0.6
Cash flow hedges	(1.7)	0.4	(5.7)	0.7
Foreign currency translation	0.0	0.1	0.0	0.2
Other comprehensive (loss) income, net of tax	(0.8)	1.6	(2.7)	4.0
Comprehensive income	$ 20.9	$ 21.5	$ 65.4	$ 64.6