Supplemental Guarantor/Non-Guarantor Financial Information (Details 1) (USD $) In Millions, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Current assets
Cash and cash equivalents	$ 558.8	$ 799.1	$ 1,295.2	$ 988.8
Accounts receivable, net	737.8	922.5
Inventories	548.4	444.4
Assets from coal trading activities, net	52.4	44.6
Deferred income taxes	56.4	27.3
Other current assets	621.7	768.0
Total current assets	2,575.5	3,005.9
Property, plant, equipment and mine development, net	11,801.7	11,251.6	7,263.3
Investments and other assets	1,431.8	2,475.5
Total assets	15,809.0	16,733.0	11,363.1
Current liabilities
Current maturities of long-term debt	47.8	101.1
Payables to (receivables from) affiliates, net	0	0
Liabilities from coal trading activities, net	19.4	10.3
Deferred income taxes	0	0
Accounts payable and accrued expenses	1,606.9	1,712.3
Total current liabilities	1,674.1	1,823.7
Long-term debt, less current maturities	6,205.1	6,556.4
Deferred income taxes	577.3	523.2
Notes payable to (receivables from) affiliates, net	0	0
Other noncurrent liabilities	2,413.7	2,313.9
Total liabilities	10,870.2	11,217.2
Peabody Energy Corporation's stockholders' equity	4,904.9	5,485.1
Noncontrolling interests	33.9	30.7
Total stockholders' equity	4,938.8	5,515.8	4,689.3	3,755.9
Total liabilities and stockholders' equity	15,809.0	16,733.0
Parent Company [Member]
Current assets
Cash and cash equivalents	269.6	283.2	903.8	368.4
Accounts receivable, net	3.6	5.3
Inventories	0	0
Assets from coal trading activities, net	0	0
Deferred income taxes	0	0
Other current assets	275.0	305.1
Total current assets	548.2	593.6
Property, plant, equipment and mine development, net	0	0
Investments and other assets	9,524.7	10,300.8
Total assets	10,072.9	10,894.4
Current liabilities
Current maturities of long-term debt	0	62.5
Payables to (receivables from) affiliates, net	2,309.3	2,417.8
Liabilities from coal trading activities, net	0	0
Deferred income taxes	3.2	11.6
Accounts payable and accrued expenses	63.3	69.4
Total current liabilities	2,375.8	2,561.3
Long-term debt, less current maturities	6,114.5	6,428.8
Deferred income taxes	43.2	76.0
Notes payable to (receivables from) affiliates, net	(3,421.3)	(3,720.0)
Other noncurrent liabilities	55.8	63.2
Total liabilities	5,168.0	5,409.3
Peabody Energy Corporation's stockholders' equity	4,904.9	5,485.1
Noncontrolling interests	0	0
Total stockholders' equity	4,904.9	5,485.1
Total liabilities and stockholders' equity	10,072.9	10,894.4
Guarantor Subsidiaries [Member]
Current assets
Cash and cash equivalents	0.3	0.8	5.2	0.2
Accounts receivable, net	5.0	100.8
Inventories	271.4	218.1
Assets from coal trading activities, net	87.5	14.9
Deferred income taxes	57.3	48.0
Other current assets	0	100.7
Total current assets	421.5	483.3
Property, plant, equipment and mine development, net	5,120.8	4,797.7
Investments and other assets	0	310.8
Total assets	5,542.3	5,591.8
Current liabilities
Current maturities of long-term debt	0	0
Payables to (receivables from) affiliates, net	(2,904.4)	(2,529.1)
Liabilities from coal trading activities, net	4.0	4.2
Deferred income taxes	0	0
Accounts payable and accrued expenses	595.0	868.8
Total current liabilities	(2,305.4)	(1,656.1)
Long-term debt, less current maturities	6.6	0
Deferred income taxes	142.0	95.3
Notes payable to (receivables from) affiliates, net	(1,100.4)	(981.5)
Other noncurrent liabilities	1,893.9	1,923.6
Total liabilities	(1,363.3)	(618.7)
Peabody Energy Corporation's stockholders' equity	6,905.6	6,210.5
Noncontrolling interests	0	0
Total stockholders' equity	6,905.6	6,210.5
Total liabilities and stockholders' equity	5,542.3	5,591.8
Non-Guarantor Subsidiaries [Member]
Current assets
Cash and cash equivalents	288.9	515.1	386.2	620.2
Accounts receivable, net	729.2	816.4
Inventories	277.0	226.3
Assets from coal trading activities, net	0	29.7
Deferred income taxes	2.3	0
Other current assets	354.6	362.2
Total current assets	1,652.0	1,949.7
Property, plant, equipment and mine development, net	6,680.9	6,453.9
Investments and other assets	1,037.0	1,496.1
Total assets	9,369.9	9,899.7
Current liabilities
Current maturities of long-term debt	47.8	38.6
Payables to (receivables from) affiliates, net	595.1	111.3
Liabilities from coal trading activities, net	50.5	6.1
Deferred income taxes	0	9.1
Accounts payable and accrued expenses	956.5	774.1
Total current liabilities	1,649.9	939.2
Long-term debt, less current maturities	84.0	127.6
Deferred income taxes	392.1	351.9
Notes payable to (receivables from) affiliates, net	4,521.7	4,701.5
Other noncurrent liabilities	464.0	327.1
Total liabilities	7,111.7	6,447.3
Peabody Energy Corporation's stockholders' equity	2,224.3	3,421.7
Noncontrolling interests	33.9	30.7
Total stockholders' equity	2,258.2	3,452.4
Total liabilities and stockholders' equity	9,369.9	9,899.7
Eliminations [Member]
Current assets
Cash and cash equivalents	0	0
Accounts receivable, net	0	0
Inventories	0	0
Assets from coal trading activities, net	(35.1)	0
Deferred income taxes	(3.2)	(20.7)
Other current assets	(7.9)	0
Total current assets	(46.2)	(20.7)
Property, plant, equipment and mine development, net	0	0
Investments and other assets	(9,129.9)	(9,632.2)
Total assets	(9,176.1)	(9,652.9)
Current liabilities
Current maturities of long-term debt	0	0
Payables to (receivables from) affiliates, net	0	0
Liabilities from coal trading activities, net	(35.1)	0
Deferred income taxes	(3.2)	(20.7)
Accounts payable and accrued expenses	(7.9)	0
Total current liabilities	(46.2)	(20.7)
Long-term debt, less current maturities	0	0
Deferred income taxes	0	0
Notes payable to (receivables from) affiliates, net	0	0
Other noncurrent liabilities	0	0
Total liabilities	(46.2)	(20.7)
Peabody Energy Corporation's stockholders' equity	(9,129.9)	(9,632.2)
Noncontrolling interests	0	0
Total stockholders' equity	(9,129.9)	(9,632.2)
Total liabilities and stockholders' equity	$ (9,176.1)	$ (9,652.9)