Segment Information (Details) (USD $) In Millions	3 Months Ended	9 Months Ended
Sep. 30, 2011	Sep. 30, 2010	Sep. 30, 2011	Sep. 30, 2010
Operating segment results
Revenues	$ 2,035.9	$ 1,864.7	$ 5,788.8	$ 5,041.7
Adjusted EBITDA	504.4	571.3	1,500.1	1,368.9
Reconciliation Of Adjusted Ebitda To Consolidated Income From Continuing Operations [Abstract]
Adjusted EBITDA	504.4	571.3	1,500.1	1,368.9
Depreciation, depletion and amortization	113.7	116.7	327.8	327.3
Asset retirement obligation expense	15.0	9.9	43.9	30.3
Interest expense	59.2	62.2	159.3	170.1
Interest income	(4.1)	(2.8)	(11.7)	(5.4)
Income tax provision	37.1	147.7	224.7	257.2
Income from continuing operations, net of income taxes	283.5	237.6	756.1	589.4
Western U.S. Mining [Member]
Operating segment results
Revenues	758.5	707.4	2,124.5	2,021.6
Adjusted EBITDA	218.7	215.7	532.2	630.9
Reconciliation Of Adjusted Ebitda To Consolidated Income From Continuing Operations [Abstract]
Adjusted EBITDA	218.7	215.7	532.2	630.9
Midwestern U.S. Mining [Member]
Operating segment results
Revenues	385.1	317.1	1,080.0	949.8
Adjusted EBITDA	104.0	77.2	295.9	222.7
Reconciliation Of Adjusted Ebitda To Consolidated Income From Continuing Operations [Abstract]
Adjusted EBITDA	104.0	77.2	295.9	222.7
Australian Mining [Member]
Operating segment results
Revenues	757.4	733.4	2,223.3	1,777.3
Adjusted EBITDA	243.3	323.2	810.7	670.1
Reconciliation Of Adjusted Ebitda To Consolidated Income From Continuing Operations [Abstract]
Adjusted EBITDA	243.3	323.2	810.7	670.1
Trading and Brokerage [Member]
Operating segment results
Revenues	131.5	101.8	329.5	273.7
Adjusted EBITDA	57.4	44.3	134.6	91.0
Reconciliation Of Adjusted Ebitda To Consolidated Income From Continuing Operations [Abstract]
Adjusted EBITDA	57.4	44.3	134.6	91.0
Corporate and Other [Member]
Operating segment results
Revenues	3.4	5.0	31.5	19.3
Adjusted EBITDA	(119.0)	(89.1)	(273.3)	(245.8)
Reconciliation Of Adjusted Ebitda To Consolidated Income From Continuing Operations [Abstract]
Adjusted EBITDA	$ (119.0)	$ (89.1)	$ (273.3)	$ (245.8)

Reconciliation of Adjusted EBITDA to consolidated income from continuing operations.

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