Segment Information (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013
Operating segment results
Revenues	$ 1,626.8	$ 1,748.0
Adjusted EBITDA	176.9	280.1
Reconciliation Of Adjusted EBITDA To Consolidated Income From Continuing Operations, Net of Income Taxes [Abstract]
Depreciation, depletion and amortization	(157.2)	(170.7)
Amortization of basis difference related to equity affiliates	(1.2)	(1.6)
Asset retirement obligation expenses	(15.6)	(19.0)
Interest expense	(103.3)	(101.3)
Interest income	3.6	5.9
Income tax benefit (provision)	52.5	(3.7)
Loss from continuing operations, net of income taxes	(44.3)	(10.3)
Australian Mining [Member]
Operating segment results
Revenues	611.8	738.0
Adjusted EBITDA	1.8	100.4
Western U.S. Mining [Member]
Operating segment results
Revenues	682.0	640.1
Adjusted EBITDA	173.9	160.5
Midwestern U.S. Mining [Member]
Operating segment results
Revenues	303.0	336.7
Adjusted EBITDA	78.7	112.3
Trading and Brokerage [Member]
Operating segment results
Revenues	21.0	25.9
Adjusted EBITDA	(1.9)	16.0
Corporate and Other [Member]
Operating segment results
Revenues	9.0	7.3
Adjusted EBITDA	$ (75.6)	$ (109.1)