Reconciliation of Segment Information, Revenue and Other Income (Details) (USD $)	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Segment Reporting, Revenue Reconciling Item [Line Items]
Total Revenue and Other Income	$ 3,299,685,000	$ 3,677,526,000	$ 4,377,045,000
Revenue From External Customers	3,120,722,000	3,282,350,000	4,237,913,000
Earnings Before Income Taxes:
Earnings Before Income Taxes	46,075,000	406,687,000	872,926,000
Acquisition and Financing Fees	0	0	(14,907,000)
Other Income	178,963,000	395,176,000	139,132,000
Total Reportable Business Segments
Earnings Before Income Taxes:
Earnings Before Income Taxes	334,910,000	631,078,000	1,162,481,000
Coal Segment [Member]
Segment Reporting, Revenue Reconciling Item [Line Items]
Total Revenue and Other Income	2,053,505,000	2,276,704,000	3,133,393,000
Earnings Before Income Taxes:
Earnings Before Income Taxes	336,524,000	591,627,000	1,032,697,000
Gas
Segment Reporting, Revenue Reconciling Item [Line Items]
Total Revenue and Other Income	810,601,000	713,163,000	823,040,000
Earnings Before Income Taxes:
Earnings Before Income Taxes	(1,614,000)	39,451,000	129,784,000
Other Segments [Member]
Segment Reporting, Revenue Reconciling Item [Line Items]
Total Revenue and Other Income	387,336,000	436,119,000	479,640,000
Earnings Before Income Taxes:
Earnings Before Income Taxes	(47,468,000)	10,997,000	3,408,000
Excludes Gas Segment [Member]
Earnings Before Income Taxes:
Interest Income (Expense), Net and Other Non-operating Activity	(226,199,000)	(228,804,000)	(258,308,000)
Acquisition and Financing Fees	0	0	14,907,000
Fees for Disposing Non-core Assets	(15,168,000)	(6,584,000)	5,780,000
Corporate Adjustments And Eliminations [Member]
Earnings Before Income Taxes:
Gain (Loss) Estimates on Extinguishment of Debt	0	0	(16,090,000)
Intersegment Eliminations [Member]
Segment Reporting, Revenue Reconciling Item [Line Items]
Total Revenue and Other Income	(130,720,000)	(143,636,000)	(198,160,000)
Earnings Before Income Taxes:
Earnings Before Income Taxes	(241,367,000)	(235,388,000)	(292,963,000)
Segment Lease Settlement	0	0	2,122,000
UNITED STATES
Segment Reporting, Revenue Reconciling Item [Line Items]
Total Revenue and Other Income	2,999,674,000	2,898,341,000	3,460,871,000
Europe [Member]
Segment Reporting, Revenue Reconciling Item [Line Items]
Total Revenue and Other Income	83,878,000	187,313,000	366,384,000
South America [Member]
Segment Reporting, Revenue Reconciling Item [Line Items]
Total Revenue and Other Income	29,787,000	169,591,000	400,307,000
CANADA
Segment Reporting, Revenue Reconciling Item [Line Items]
Total Revenue and Other Income	3,575,000	5,692,000	10,351,000
Other Credit Derivatives [Member]
Segment Reporting, Revenue Reconciling Item [Line Items]
Total Revenue and Other Income	$ 3,808,000	$ 21,413,000	$ 0