Statements of Consolidated Comprehensive Income - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Statement of Comprehensive Income [Abstract]
Net income (loss)	$ 14.9	$ 22.1	$ 67.2	$ (249.9)
Reclassification adjustments:
Amortization of net actuarial loss	0.1	0.3	0.3	0.8
Amortization of prior service cost	1.0	0.7	3.0	2.2
Removal of obligation relating to Union VEBA	0.0	0.0	0.0	106.6
Other comprehensive income relating to VEBAs	1.1	1.0	3.3	109.6
Unrealized gain (loss) on available for sale securities	0.9	(0.4)	1.3	(0.7)
Available for sale securities:
Reclassification of unrealized (gain) loss upon sale of available for sale securities	(0.3)	(0.1)	(0.3)	0.1
Other comprehensive income (loss) relating to available for sale securities	0.6	(0.5)	1.0	(0.6)
Translation gain on Canadian pension plan accumulated other comprehensive income balance	0.0	0.0	0.1	0.0
Unrealized gain (loss) on foreign currency cash flow hedges	0.1	0.0	0.2	(0.2)
Foreign currency translation loss	0.0	(0.3)	0.0	(0.2)
Other comprehensive income, before tax	1.8	0.2	4.6	108.6
Income tax expense related to items of other comprehensive income	(0.7)	(0.1)	(1.7)	(41.2)
Other comprehensive income, net of tax	1.1	0.1	2.9	67.4
Comprehensive income (loss)	$ 16.0	$ 22.2	$ 70.1	$ (182.5)