Accumulated Other Comprehensive Income (Loss) (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
After-tax components of comprehensive income (loss)
Foreign Currency Translation Adjustment, Beginning Balance	$ 3.1	$ 3.1	$ 3.1
Foreign Currency Translation Adjustment, Ending Balance	3.1	3.1	3.1
Net Actuarial Loss Associated with Postretirement Plans and Workers' Compensation Obligations, Beginning Balance	(353.0)	(343.5)	(220.4)
Net Actuarial Loss Associated with Postretirement Plans and Workers' Compensation Obligations, Reclassifications	(38.2)	(31.8)	(11.8)
Net Actuarial Loss Associated with Postretirement Plans and Workers' Compensation Obligations, Current period change	(150.1)	(41.3)	(134.9)
Net Actuarial Loss Associated with Postretirement Plans and Workers' Compensation Obligations, Ending Balance	(464.9)	(353.0)	(343.5)
Prior Service Cost Associated with Postretirement Plans, Beginning Balance	(12.8)	(10.4)	(18.7)
Prior Service Cost Associated with Postretirement Plans, Reclassification	(2.3)	(2.5)	(1.8)
Prior Service Cost Associated with Postretirement Plans, Current period change	0.9	(4.9)	6.5
Prior Service Cost Associated with Postretirement Plans, Ending Balance	(9.6)	(12.8)	(10.4)
Cash Flow Hedges, Beginning Balance	294.8	167.3	(152.5)
Cash Flow Hedges, Net change in fair value	291.9	229.9	235.2
Cash Flow Hedges, Reclassification	(251.0)	(102.4)	84.6
Cash Flow Hedges, Ending Balance	335.7	294.8	167.3
Available-For-Sale Securities Adjustment, Beginning Balance	0	0	0
Available-For-Sale Securities Adjustment, Net change in fair value	(5.8)	0	0
Available-For-Sale Securities Adjustment, Reclassification	0.9	0	0
Available-For-Sale Securities Adjustment, Ending Balance	(6.7)	0	0
Total Accumulated Other Comprehensive Loss, Beginning Balance	(67.9)	(183.5)	(388.5)
Total Accumulated Other Comprehensive Loss, Net change in fair value	286.1	229.9	235.2
Total Accumulated Other Comprehensive Loss, Reclassification	(211.4)	(68.1)	98.2
Total Accumulated Other Comprehensive Loss, Current period change net of tax	(149.2)	(46.2)	(128.4)
Total Accumulated Other Comprehensive Loss, Ending Balance	$ (142.4)	$ (67.9)	$ (183.5)