Other Comprehensive Income (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013
Reclassification adjustments, before tax:
Amortization of net actuarial (gain) loss, before tax	$ (0.3)	$ 0.3
Amortization of prior service cost, before tax	2.8	1.1
Other comprehensive income relating to VEBAs, before tax	2.5	1.4
Available for sale securities
Unrealized gain on available for sale securities, before tax	0.1	0.3
Reclassification adjustments, before tax:
Reclassification of unrealized gain upon sale of available for sale securities, before tax	(0.1)	(0.4)
Other comprehensive income (loss) relating to available for sale securities, before tax	0	(0.1)
Foreign currency translation adjustment, before tax	0.2	0.4
Cumulative tax rate adjustment, before tax	0
Other comprehensive income, before tax	2.7	1.7
Reclassification adjustments, income tax (expense) benefit:
Amortization of net actuarial (gain) loss, income tax (expense) benefit	0.1	(0.1)
Amortization of prior service cost, income tax (expense) benefit	(1.0)	(0.4)
Other comprehensive income relating to VEBAs, income tax (expense) benefit	(0.9)	(0.5)
Available for sale securities
Unrealized gain on available for sale securities, Income tax (expense) benefit	0	(0.1)
Reclassification adjustments, income tax (expense) benefit:
Reclassification of unrealized gain upon sale of available for sale securities, income tax (expense) benefit	0	0.1
Other comprehensive income (loss) relating to available for sale securities, income tax (expense)	0	0
Foreign currency translation adjustment, income tax (expense) benefit	0	0
Cumulative tax rate adjustment, tax	(0.9)
Other comprehensive income, Income tax (expense) benefit	(1.8)	(0.5)
Reclassification adjustments, net of tax:
Amortization of net actuarial (gain) loss relating to VEBAs, net of tax	(0.2)	0.2
Amortization of prior service cost relating to VEBAs, net of tax	1.8	0.7
Other comprehensive income relating to VEBAs, net of tax	1.6	0.9
Available for sale securities
Unrealized gain on available for sale securities, net of tax	0.1	0.2
Reclassification adjustments, net of tax:
Reclassification of unrealized gain upon sale of available for sale securities, net of tax	(0.1)	(0.3)
Other comprehensive income (loss) relating to available for sale securities, net of tax	0	(0.1)
Foreign currency translation adjustment, net of tax	0.2	0.4
Cumulative tax rate adjustment, net of tax	(0.9)
Other comprehensive income, net of tax	$ 0.9	$ 1.2