Statements of Consolidated Comprehensive Income (Loss) (USD $) In Millions, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Net income	$ 27.3	$ 25.4	$ 18.6	$ 33.5	$ 9.1	$ 29.2	$ 21.0	$ 26.5	$ 104.8	$ 85.8	$ 25.1
Defined benefit pension plan and VEBAs
Net actuarial gain (loss) arising during the period									2.2	87.8	(110.6)
Reclassification adjustments relating to VEBAs:
Amortization of net actuarial loss									1.5	3.1	0.6
Amortization of prior service cost									4.2	4.2	4.2
Other comprehensive income (loss) relating to defined benefit pension plan and VEBAs									7.9	95.1	(105.8)
Available for sale securities
Unrealized gain (loss) 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), before tax									8.1	95.5	(105.7)
Income tax (expense) benefit related to items of other comprehensive income (loss)									(2.8)	(36.5)	40.4
Other comprehensive income (loss), net of tax									5.3	59.0	(65.3)
Comprehensive income (loss)									$ 110.1	$ 144.8	$ (40.2)