Annual report pursuant to Section 13 and 15(d)

CASH FLOW INFORMATION (Reconciliation Of Capital Additions To Cash Paid For Capital Expenditures) (Details)

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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.