Maximum Potential Total of Future Payments Under Commitment Instruments (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2014
Loss Contingencies [Line Items]
Loss Contingency, Range of Possible Loss, Portion Not Accrued	388,986
Maximum potential total of future payments under commitments	1,346,712
Ratliff [Member]
Loss Contingencies [Line Items]
Loss Contingency, Damages Sought	50000
Surety Bond [Member]
Loss Contingencies [Line Items]
Maximum potential total of future payments under commitments	304,648
Surety Bond [Member] | Employee-Related
Loss Contingencies [Line Items]
Maximum potential total of future payments under commitments	150,042
Surety Bond [Member] | Environmental
Loss Contingencies [Line Items]
Maximum potential total of future payments under commitments	5,509
Surety Bond [Member] | Other Commitments
Loss Contingencies [Line Items]
Maximum potential total of future payments under commitments	149,097
Surety Bonds:
Loss Contingencies [Line Items]
Maximum potential total of future payments under commitments	846,893
Surety Bonds: | Employee-Related
Loss Contingencies [Line Items]
Maximum potential total of future payments under commitments	223,579
Surety Bonds: | Environmental
Loss Contingencies [Line Items]
Maximum potential total of future payments under commitments	598,877
Surety Bonds: | Other Commitments
Loss Contingencies [Line Items]
Maximum potential total of future payments under commitments	24,437
Guarantees [Member]
Loss Contingencies [Line Items]
Maximum potential total of future payments under commitments	195,171
Guarantees [Member] | Other Commitments
Loss Contingencies [Line Items]
Maximum potential total of future payments under commitments	61,571
Guarantees [Member] | Coal Segment [Member]
Loss Contingencies [Line Items]
Maximum potential total of future payments under commitments	133,600
Earl Kennedy [Member]
Loss Contingencies [Line Items]
Loss Contingency, Damages Sought	20000
Balance on First Anniversary [Member]
Loss Contingencies [Line Items]
Maximum potential total of future payments under commitments	1,253,448
Balance on First Anniversary [Member] | Surety Bond [Member]
Loss Contingencies [Line Items]
Maximum potential total of future payments under commitments	271,382
Balance on First Anniversary [Member] | Surety Bond [Member] | Employee-Related
Loss Contingencies [Line Items]
Maximum potential total of future payments under commitments	124,536
Balance on First Anniversary [Member] | Surety Bond [Member] | Environmental
Loss Contingencies [Line Items]
Maximum potential total of future payments under commitments	5,509
Balance on First Anniversary [Member] | Surety Bond [Member] | Other Commitments
Loss Contingencies [Line Items]
Maximum potential total of future payments under commitments	141,337
Balance on First Anniversary [Member] | Surety Bonds:
Loss Contingencies [Line Items]
Maximum potential total of future payments under commitments	846,892
Balance on First Anniversary [Member] | Surety Bonds: | Employee-Related
Loss Contingencies [Line Items]
Maximum potential total of future payments under commitments	223,579
Balance on First Anniversary [Member] | Surety Bonds: | Environmental
Loss Contingencies [Line Items]
Maximum potential total of future payments under commitments	598,877
Balance on First Anniversary [Member] | Surety Bonds: | Other Commitments
Loss Contingencies [Line Items]
Maximum potential total of future payments under commitments	24,436
Balance on First Anniversary [Member] | Guarantees [Member]
Loss Contingencies [Line Items]
Maximum potential total of future payments under commitments	135,174
Balance on First Anniversary [Member] | Guarantees [Member] | Other Commitments
Loss Contingencies [Line Items]
Maximum potential total of future payments under commitments	34,974
Balance on First Anniversary [Member] | Guarantees [Member] | Coal Segment [Member]
Loss Contingencies [Line Items]
Maximum potential total of future payments under commitments	100,200
More Than One And Within Three Years From Balance Sheet Date [Member]
Loss Contingencies [Line Items]
Maximum potential total of future payments under commitments	75,488
More Than One And Within Three Years From Balance Sheet Date [Member] | Surety Bond [Member]
Loss Contingencies [Line Items]
Maximum potential total of future payments under commitments	33,266
More Than One And Within Three Years From Balance Sheet Date [Member] | Surety Bond [Member] | Employee-Related
Loss Contingencies [Line Items]
Maximum potential total of future payments under commitments	25,506
More Than One And Within Three Years From Balance Sheet Date [Member] | Surety Bond [Member] | Environmental
Loss Contingencies [Line Items]
Maximum potential total of future payments under commitments	0
More Than One And Within Three Years From Balance Sheet Date [Member] | Surety Bond [Member] | Other Commitments
Loss Contingencies [Line Items]
Maximum potential total of future payments under commitments	7,760
More Than One And Within Three Years From Balance Sheet Date [Member] | Surety Bonds:
Loss Contingencies [Line Items]
Maximum potential total of future payments under commitments	0
More Than One And Within Three Years From Balance Sheet Date [Member] | Surety Bonds: | Employee-Related
Loss Contingencies [Line Items]
Maximum potential total of future payments under commitments	0
More Than One And Within Three Years From Balance Sheet Date [Member] | Surety Bonds: | Environmental
Loss Contingencies [Line Items]
Maximum potential total of future payments under commitments	0
More Than One And Within Three Years From Balance Sheet Date [Member] | Surety Bonds: | Other Commitments
Loss Contingencies [Line Items]
Maximum potential total of future payments under commitments	0
More Than One And Within Three Years From Balance Sheet Date [Member] | Guarantees [Member]
Loss Contingencies [Line Items]
Maximum potential total of future payments under commitments	42,222
More Than One And Within Three Years From Balance Sheet Date [Member] | Guarantees [Member] | Other Commitments
Loss Contingencies [Line Items]
Maximum potential total of future payments under commitments	8,822
More Than One And Within Three Years From Balance Sheet Date [Member] | Guarantees [Member] | Coal Segment [Member]
Loss Contingencies [Line Items]
Maximum potential total of future payments under commitments	33,400
More Than Three And Within Five Years From Balance Sheet Date [Member]
Loss Contingencies [Line Items]
Maximum potential total of future payments under commitments	8,367
More Than Three And Within Five Years From Balance Sheet Date [Member] | Surety Bond [Member]
Loss Contingencies [Line Items]
Maximum potential total of future payments under commitments	0
More Than Three And Within Five Years From Balance Sheet Date [Member] | Surety Bond [Member] | Employee-Related
Loss Contingencies [Line Items]
Maximum potential total of future payments under commitments	0
More Than Three And Within Five Years From Balance Sheet Date [Member] | Surety Bond [Member] | Environmental
Loss Contingencies [Line Items]
Maximum potential total of future payments under commitments	0
More Than Three And Within Five Years From Balance Sheet Date [Member] | Surety Bond [Member] | Other Commitments
Loss Contingencies [Line Items]
Maximum potential total of future payments under commitments	0
More Than Three And Within Five Years From Balance Sheet Date [Member] | Surety Bonds:
Loss Contingencies [Line Items]
Maximum potential total of future payments under commitments	0
More Than Three And Within Five Years From Balance Sheet Date [Member] | Surety Bonds: | Employee-Related
Loss Contingencies [Line Items]
Maximum potential total of future payments under commitments	0
More Than Three And Within Five Years From Balance Sheet Date [Member] | Surety Bonds: | Environmental
Loss Contingencies [Line Items]
Maximum potential total of future payments under commitments	0
More Than Three And Within Five Years From Balance Sheet Date [Member] | Surety Bonds: | Other Commitments
Loss Contingencies [Line Items]
Maximum potential total of future payments under commitments	0
More Than Three And Within Five Years From Balance Sheet Date [Member] | Guarantees [Member]
Loss Contingencies [Line Items]
Maximum potential total of future payments under commitments	8,367
More Than Three And Within Five Years From Balance Sheet Date [Member] | Guarantees [Member] | Other Commitments
Loss Contingencies [Line Items]
Maximum potential total of future payments under commitments	8,367
More Than Three And Within Five Years From Balance Sheet Date [Member] | Guarantees [Member] | Coal Segment [Member]
Loss Contingencies [Line Items]
Maximum potential total of future payments under commitments	0
Beyond Five Years of Balance Sheet Date [Member]
Loss Contingencies [Line Items]
Maximum potential total of future payments under commitments	9,409
Beyond Five Years of Balance Sheet Date [Member] | Surety Bond [Member]
Loss Contingencies [Line Items]
Maximum potential total of future payments under commitments	0
Beyond Five Years of Balance Sheet Date [Member] | Surety Bond [Member] | Employee-Related
Loss Contingencies [Line Items]
Maximum potential total of future payments under commitments	0
Beyond Five Years of Balance Sheet Date [Member] | Surety Bond [Member] | Environmental
Loss Contingencies [Line Items]
Maximum potential total of future payments under commitments	0
Beyond Five Years of Balance Sheet Date [Member] | Surety Bond [Member] | Other Commitments
Loss Contingencies [Line Items]
Maximum potential total of future payments under commitments	0
Beyond Five Years of Balance Sheet Date [Member] | Surety Bonds:
Loss Contingencies [Line Items]
Maximum potential total of future payments under commitments	1
Beyond Five Years of Balance Sheet Date [Member] | Surety Bonds: | Employee-Related
Loss Contingencies [Line Items]
Maximum potential total of future payments under commitments	0
Beyond Five Years of Balance Sheet Date [Member] | Surety Bonds: | Environmental
Loss Contingencies [Line Items]
Maximum potential total of future payments under commitments	0
Beyond Five Years of Balance Sheet Date [Member] | Surety Bonds: | Other Commitments
Loss Contingencies [Line Items]
Maximum potential total of future payments under commitments	1
Beyond Five Years of Balance Sheet Date [Member] | Guarantees [Member]
Loss Contingencies [Line Items]
Maximum potential total of future payments under commitments	9,408
Beyond Five Years of Balance Sheet Date [Member] | Guarantees [Member] | Other Commitments
Loss Contingencies [Line Items]
Maximum potential total of future payments under commitments	9,408
Beyond Five Years of Balance Sheet Date [Member] | Guarantees [Member] | Coal Segment [Member]
Loss Contingencies [Line Items]
Maximum potential total of future payments under commitments	0