Statements of Consolidated Comprehensive Income (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013
Statement of Comprehensive Income [Abstract]
Net income	$ 15.8	$ 33.5
Reclassification adjustments:
Amortization of net actuarial (gain) loss	(0.3)	0.3
Amortization of prior service cost	2.8	1.1
Other comprehensive income relating to VEBAs	2.5	1.4
Available for sale securities
Unrealized gain on available for sale securities	0.1	0.3
Reclassification adjustments:
Reclassification of unrealized gain upon sale of available for sale securities	(0.1)	(0.4)
Other comprehensive income (loss) relating to available for sale securities	0	(0.1)
Foreign currency translation adjustment	0.2	0.4
Other comprehensive income, before tax	2.7	1.7
Income tax expense related to items of other comprehensive income	(1.8)	(0.5)
Other comprehensive income, net of tax	0.9	1.2
Comprehensive income	$ 16.7	$ 34.7