Other Comprehensive Income (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Reclassification adjustments, before tax:
Amortization of net actuarial (gain) loss, before tax	$ 0.2	$ (0.6)	$ 0.5	$ (0.9)
Amortization of prior service cost, before tax	0.8	2.6	1.5	5.4
Removal of obligation relating to Union VEBA	0.0	0.0	106.6	0.0
Other comprehensive income relating to VEBAs, before tax	1.0	2.0	108.6	4.5
Available for sale securities:
Unrealized gain on available for sale securities, before tax	(0.3)	0.2	(0.3)	0.3
Reclassification of unrealized gain upon sale of available for sale securities, before tax	0.1	(0.1)	0.2	(0.2)
Other comprehensive income (loss) relating to available for sale securities	(0.2)	0.1	(0.1)	0.1
Unrealized Gain (Loss) on Foreign Currency Derivatives, Net, before Tax	(0.2)	0.0	(0.2)	0.0
Foreign currency translation adjustment, before tax	0.0	(0.1)	0.1	0.1
Other Comprehensive Income Cumulative Tax Rate Adjustments Before Tax		0.0
Other comprehensive income, before tax	0.6	2.0	108.4	4.7
Reclassification adjustments, income tax (expense) benefit:
Amortization of net actuarial (gain) loss, income tax (expense) benefit	(0.1)	0.2	(0.2)	0.3
Amortization of prior service cost, income tax (expense) benefit	(0.3)	(1.0)	(0.6)	(2.0)
Other Comprehensive Income (Loss), Finalization of Pension and Other Postretirement Benefit Plan Valuation, Tax			(40.4)
Other comprehensive income relating to VEBAs, income tax (expense) benefit	(0.4)	(0.8)	(41.2)	(1.7)
Available for sale securities:
Unrealized loss on available for sale securities	0.1	(0.1)	0.1	(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	0.1	(0.1)	0.1
Other comprehensive income (loss) relating to available for sale securities, income tax (expense) benefit	0.1	0.0	0.0	0.0
Other Comprehensive Income (Loss), Derivatives Qualifying as Hedges, Tax	0.1		0.1
Foreign currency translation adjustment, income tax (expense) benefit		0.0	0.0	0.0
Other Comprehensive Income Cumulative Tax Rate Adjustments Tax		0.9
Other comprehensive income, Income tax (expense) benefit	(0.2)	0.1	(41.1)	(1.7)
Reclassification adjustments, net of tax:
Amortization of net actuarial (gain) loss, net of tax	0.1	(0.4)	0.3	(0.6)
Amortization of prior service cost, net of tax	0.5	1.6	0.9	3.4
Other Comprehensive Income (Loss), Finalization of Pension and Other Postretirement Benefit Plan Valuation, Net of Tax			66.2
Other comprehensive income relating to VEBAs, net of tax	0.6	1.2	67.4	2.8
Available for sale securities:
Unrealized gain on available for sale securities, net of tax	(0.2)	0.1	(0.2)	0.2
Reclassification adjustments, net of tax:
Reclassification of unrealized gain upon sale of available for sale securities, net of tax	0.1	0.0	0.1	(0.1)
Other comprehensive income (loss) relating to available for sale securities, net of tax	(0.1)	0.1	(0.1)	0.1
Other Comprehensive Income (Loss), Derivatives Qualifying as Hedges, Net of Tax	(0.1)		(0.1)
Foreign currency translation adjustment, net of tax		(0.1)	0.1	0.1
Other Comprehensive Income Cumulative Tax Rate Adjustments Net of Tax		0.9
Other comprehensive income, net of tax	$ 0.4	$ 2.1	$ 67.3	$ 3.0