Other Comprehensive Income (Loss) (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Defined benefit pension plan and VEBAs:
Net actuarial (loss) gain arising during the period	$ 2.2	$ 87.8	$ (110.6)
Reclassification adjustments:
Less: amortization of net actuarial loss	1.5	3.1	0.6
Less: amortization of prior service cost	4.2	4.2	4.2
Other comprehensive income relating to defined benefit pension plan and VEBAs	7.9	95.1	(105.8)
Available for Sale Securities:
Unrealized gain on available for sale securities	1.0	0.6	(0.1)
Reclassification adjustments:
Less: reclassification of unrealized gain upon sale of available for sale securities	(1.0)	0	0
Other comprehensive income (loss) relating to available for sale securities	0	0.6	(0.1)
Foreign currency translation adjustment	0.2	(0.2)	0.2
Other comprehensive income (loss)	8.1	95.5	(105.7)
Defined benefit pension plan and VEBAs:
Net actuarial (loss) gain arising during the period	(0.7)	(33.5)	42.2
Reclassification adjustments:
Less: amortization of net actuarial loss	(0.5)	(1.1)	(0.2)
Less: amortization of prior service cost	(1.6)	(1.7)	(1.6)
Other comprehensive income relating to defined benefit pension plan and VEBAs	(2.8)	(36.3)	40.4
Available for Sale Securities:
Unrealized gain on available for sale securities	(0.3)	(0.2)	0
Reclassification adjustments:
Less: reclassification of unrealized gain upon sale of available for sale securities	0.3
Other comprehensive income (loss) relating to available for sale securities	0
Foreign currency translation adjustment	0	0	0
Other comprehensive income (loss)	(2.8)	(36.5)	40.4
Defined benefit pension plan and VEBAs:
Net actuarial (loss) gain arising during the period	1.5	54.3	(68.4)
Reclassification adjustments:
Less: amortization of net actuarial loss	1.0	2.0	0.4
Less: amortization of prior service cost	2.6	2.5	2.6
Other comprehensive income relating to defined benefit pension plan and VEBAs	5.1	58.8	(65.4)
Available for Sale Securities:
Unrealized gain on available for sale securities	0.7	0.4	(0.1)
Reclassification adjustments:
Less: reclassification of unrealized gain upon sale of available for sale securities	(0.7)
Other comprehensive income (loss) relating to available for sale securities	0
Foreign currency translation adjustment	0.2	(0.2)	0.2
Other comprehensive income (loss), net of tax	$ 5.3	$ 59.0	$ (65.3)