Statements of Consolidated Comprehensive Income Statements of Comprehensive Income - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Net income	$ 36.0	$ 26.3
Other Comprehensive Income (Loss), Net of Tax - Note 13:
Defined benefit pension plan and VEBAs	0.9	0.8
Available for sale securities	0.1	0.0
Other comprehensive income, net of tax	1.3	0.9
Comprehensive income	37.3	27.2
Foreign Exchange Contract [Member]
Other Comprehensive Income (Loss), Net of Tax - Note 13:
Foreign currency and alloy hedges	0.1	0.1
Alloy Metal Hedge [Member]
Other Comprehensive Income (Loss), Net of Tax - Note 13:
Foreign currency and alloy hedges	$ 0.2	$ 0.0