Other Comprehensive Income (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended				9 Months Ended
	Sep. 30, 2014		Sep. 30, 2013		Sep. 30, 2014		Sep. 30, 2013
Reclassification adjustments, before tax:
Amortization of net actuarial (gain) loss, before tax	$ (0.5)	[1]	$ 0.3	[1]	$ (1.4)	[1]	$ 1.0	[1]
Amortization of prior service cost, before tax	2.6	[1]	1.0	[1]	8.0	[1]	3.1	[1]
Other comprehensive income relating to VEBAs, before tax	(2.1)		(1.3)		(6.6)		(4.1)
Available for sale securities:
Unrealized gain on available for sale securities, before tax	0.2		(0.4)		(0.1)		(0.9)
Reclassification adjustments, before tax:
Reclassification of unrealized gain upon sale of available for sale securities, before tax	0	[2]	(0.2)	[2]	(0.2)	[2]	(0.8)	[2]
Other comprehensive income (loss) relating to available for sale securities	(0.2)		0.2		(0.1)		0.1
Foreign currency translation adjustment, before tax	(0.1)		0.3		(0.2)		(0.5)
Other comprehensive income, before tax	2.0		1.2		6.7		4.7
Reclassification adjustments, income tax (expense) benefit:
Amortization of net actuarial (gain) loss, income tax (expense) benefit	0.2	[1],[3]	(0.2)	[1],[3]	0.5	[1],[3]	(0.4)	[1],[3]
Amortization of prior service cost, income tax (expense) benefit	(1.0)	[1],[3]	(0.4)	[1],[3]	(3.0)	[1],[3]	(1.2)	[1],[3]
Other comprehensive income relating to VEBAs, income tax (expense) benefit	(0.8)		(0.6)		(2.5)		(1.6)
Available for sale securities:
Unrealized gain on available for sale securities, Income tax (expense) benefit			(0.1)		0	[3]	(0.3)	[3]
Reclassification adjustments, income tax (expense) benefit:
Reclassification of unrealized gain upon sale of available for sale securities, income tax (expense) benefit			0.1	[2],[3]	0.1	[2],[3]	0.3	[2],[3]
Other comprehensive income (loss) relating to available for sale securities, income tax (expense) benefit	0.1	[3]	0		0.1		0
Foreign currency translation adjustment, income tax (expense) benefit	0	[3]	0	[3]	0	[3]	0	[3]
Other comprehensive income, Income tax (expense) benefit	(0.7)	[3]	(0.6)	[3]	(2.4)	[3]	(1.6)	[3]
Reclassification adjustments, net of tax:
Amortization of net actuarial (gain) loss, net of tax	(0.3)	[1]	0.1	[1]	(0.9)	[1]	0.6	[1]
Amortization of prior service cost, net of tax	1.6	[1]	0.6	[1]	5.0	[1]	1.9	[1]
Other comprehensive income relating to VEBAs, net of tax	1.3		0.7		4.1		2.5
Available for sale securities:
Unrealized gain on available for sale securities, net of tax			0.3		0.1		0.6
Reclassification adjustments, net of tax:
Reclassification of unrealized gain upon sale of available for sale securities, net of tax			(0.1)	[2]	(0.1)	[2]	(0.5)	[2]
Other comprehensive income (loss) relating to available for sale securities, net of tax	(0.1)		0.2		0		0.1
Foreign currency translation adjustment, net of tax	0.1		(0.3)		0.2		0.5
Other comprehensive income, net of tax	$ 1.3		$ 0.6		$ 4.3		$ 3.1

[1] Amounts reclassified out of Accumulated other comprehensive income relating to VEBA adjustments were included as a component of Net periodic pension benefit income relating to VEBAs.

[2] Amounts reclassified out of Accumulated other comprehensive income relating to sales of available for sale securities were included as a component of Other income (expense), net. The Company uses the specific identification method to determine the amount reclassified out of accumulated other comprehensive income.

[3] Income tax amounts reclassified out of Accumulated other comprehensive income relating to VEBA adjustments and sales of available for sale securities were included as a component of Income tax provision.