Cash Flow Information (Reconciliation Of Capital Additions To Cash Paid For Capital Expenditures) (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended						1 Months Ended
	Dec. 31, 2011		Dec. 31, 2010		Dec. 31, 2009		Oct. 31, 2011 Pinnacle [Member]	Dec. 31, 2010 Pinnacle [Member]
Capital additions	$ 960.9		$ 275.8		$ 168.2
Cash paid for capital expenditures	862.1	[1]	209.6	[1]	116.3	[1]
Difference	98.8		66.2		51.9
Non-cash accruals	60.1		8.9		3.0
Capital leases	38.7		57.3		48.9
Total	98.8		66.2		51.9
Cash proceeds from sale-leaseback							$ 18.6	$ 57.3

[1] Cash paid for capital expenditures for 2011 and 2010 has been shown net of cash proceeds of $18.6 and $57.3 million, respectively, from the Pinnacle longwall sale- leaseback that was completed in October 2011 and December 2010. The adjustment was necessary in 2011 and 2010 due to the timing of the cash payments i related to the longwall.