Statements of Consolidated Comprehensive Income - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
Statement of Comprehensive Income [Abstract]
Net income	$ 26.3	$ (292.2)
Reclassification adjustments:
Amortization of net actuarial loss	0.1	0.3
Amortization of prior service cost	1.0	0.7
Removal of obligation relating to Union VEBA	0.0	106.6
Other comprehensive income relating to VEBAs	(1.1)	(107.6)
Available for sale securities:
Reclassification of unrealized loss upon sale of available for sale securities	0.0	(0.1)
Other comprehensive income relating to available for sale securities	0.0	0.1
Foreign currency translation gain on Canadian pension plan	0.1	0.0
Unrealized gain on foreign currency cash flow hedges	0.2	0.0
Foreign currency translation gain	0.0	0.1
Other comprehensive income, before tax	1.4	107.8
Income tax expense related to items of other comprehensive income	(0.5)	(40.9)
Other comprehensive income, net of tax	0.9	66.9
Comprehensive income (loss)	$ 27.2	$ (225.3)