CASH FLOW INFORMATION (Reconciliation Of Capital Additions To Cash Paid For Capital Expenditures) (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012		Dec. 31, 2011		Dec. 31, 2010
Related Party Transaction [Line Items]
Capital additions	$ 1,335.3	[1]	$ 960.9	[1]	$ 275.8	[1]
Cash paid for capital expenditures	1,127.5	[2]	862.1	[2]	209.6	[2]
Non-cash accruals	152.5		60.1		8.9
Capital leases	55.3		38.7		57.3
Total	207.8		98.8		66.2
Pinnacle [Member]
Related Party Transaction [Line Items]
Cash proceeds from sale-leaseback			$ 18.6		$ 57.3

[1] Includes capital lease additions and non-cash accruals. Refer to NOTE 21 - CASH FLOW INFORMATION

[2] Cash paid for capital expenditures for 2011 and 2010 has been shown net of cash proceeds of $18.6 million 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 related to the longwall.