Supplemental Guarantor/Non-Guarantor Financial Information (Details 1) (USD $) In Millions	Sep. 30, 2011	Dec. 31, 2010	Sep. 30, 2010	Dec. 31, 2009
Current assets
Cash and cash equivalents	$ 1,401.6	$ 1,295.2	$ 1,367.5	$ 988.8
Accounts receivable, net	591.4	558.2
Inventories	351.9	332.9
Assets from coal trading activities, net	66.0	192.5
Deferred income taxes	90.9	120.4
Other current assets	503.2	459.0
Total current assets	3,005.0	2,958.2
Property, plant, equipment and mine development, net	7,808.1	7,426.1
Deferred income taxes	0
Investments and other assets	878.5	978.8
Total assets	11,691.6	11,363.1
Current liabilities
Current maturities of long-term debt	43.8	43.2
Payables to (receivables from) affiliates, net	0	0
Liabilities from coal trading activities, net	62.6	181.7
Deferred income taxes	0	0
Accounts payable and accrued expenses	1,334.9	1,288.8
Total current liabilities	1,441.3	1,513.7
Long-term debt, less current maturities	2,458.6	2,706.8
Deferred income taxes	499.6	539.8
Notes payable to (receivables from) affiliates, net	0	0
Other noncurrent liabilities	1,969.6	1,913.5
Total liabilities	6,369.1	6,673.8
Peabody Energy Corporation's stockholders' equity	5,289.0	4,660.7
Noncontrolling interests	33.5	28.6
Total stockholders' equity	5,322.5	4,689.3
Total liabilities and stockholders' equity	11,691.6	11,363.1
Parent Company [Member]
Current assets
Cash and cash equivalents	957.9	903.8	481.3	368.4
Accounts receivable, net	4.6	2.1
Inventories	0	0
Assets from coal trading activities, net	0	0
Deferred income taxes	0	0
Other current assets	281.2	307.9
Total current assets	1,243.7	1,213.8
Property, plant, equipment and mine development, net	0	0
Deferred income taxes	3.1
Investments and other assets	9,845.7	9,331.0
Total assets	11,092.5	10,544.8
Current liabilities
Current maturities of long-term debt	25.0	25.0
Payables to (receivables from) affiliates, net	2,445.3	2,225.3
Liabilities from coal trading activities, net	0	0
Deferred income taxes	6.1	6.1
Accounts payable and accrued expenses	67.5	47.4
Total current liabilities	2,543.9	2,303.8
Long-term debt, less current maturities	2,372.0	2,609.6
Deferred income taxes	0	93.2
Notes payable to (receivables from) affiliates, net	819.1	818.9
Other noncurrent liabilities	68.5	58.6
Total liabilities	5,803.5	5,884.1
Peabody Energy Corporation's stockholders' equity	5,289.0	4,660.7
Noncontrolling interests	0	0
Total stockholders' equity	5,289.0	4,660.7
Total liabilities and stockholders' equity	11,092.5	10,544.8
Guarantor Subsidiaries [Member]
Current assets
Cash and cash equivalents	1.0	5.2	0.1	0.2
Accounts receivable, net	53.8	5.5
Inventories	204.3	168.0
Assets from coal trading activities, net	16.1	23.8
Deferred income taxes	62.6	78.6
Other current assets	77.8	30.7
Total current assets	415.6	311.8
Property, plant, equipment and mine development, net	4,801.4	4,732.7
Deferred income taxes	0
Investments and other assets	204.5	179.8
Total assets	5,421.5	5,224.3
Current liabilities
Current maturities of long-term debt	0	0
Payables to (receivables from) affiliates, net	(2,621.7)	(2,528.3)
Liabilities from coal trading activities, net	8.8	29.5
Deferred income taxes	0	0
Accounts payable and accrued expenses	740.6	777.2
Total current liabilities	(1,872.3)	(1,721.6)
Long-term debt, less current maturities	0.1	0.1
Deferred income taxes	193.7	135.4
Notes payable to (receivables from) affiliates, net	(823.6)	(825.3)
Other noncurrent liabilities	1,670.9	1,652.8
Total liabilities	(831.2)	(758.6)
Peabody Energy Corporation's stockholders' equity	6,252.7	5,982.9
Noncontrolling interests	0	0
Total stockholders' equity	6,252.7	5,982.9
Total liabilities and stockholders' equity	5,421.5	5,224.3
Non-Guarantor Subsidiaries [Member]
Current assets
Cash and cash equivalents	442.7	386.2	886.1	620.2
Accounts receivable, net	533.0	550.6
Inventories	147.6	164.9
Assets from coal trading activities, net	49.9	168.7
Deferred income taxes	34.4	47.9
Other current assets	144.2	120.4
Total current assets	1,351.8	1,438.7
Property, plant, equipment and mine development, net	3,006.7	2,693.4
Deferred income taxes	0
Investments and other assets	155.2	99.1
Total assets	4,513.7	4,231.2
Current liabilities
Current maturities of long-term debt	18.8	18.2
Payables to (receivables from) affiliates, net	176.4	303.0
Liabilities from coal trading activities, net	53.8	152.2
Deferred income taxes	0	0
Accounts payable and accrued expenses	526.8	464.2
Total current liabilities	775.8	937.6
Long-term debt, less current maturities	86.5	97.1
Deferred income taxes	309.0	311.2
Notes payable to (receivables from) affiliates, net	4.5	6.4
Other noncurrent liabilities	230.2	202.1
Total liabilities	1,406.0	1,554.4
Peabody Energy Corporation's stockholders' equity	3,074.2	2,648.2
Noncontrolling interests	33.5	28.6
Total stockholders' equity	3,107.7	2,676.8
Total liabilities and stockholders' equity	4,513.7	4,231.2
Eliminations [Member]
Current assets
Cash and cash equivalents	0	0
Accounts receivable, net	0	0
Inventories	0	0
Assets from coal trading activities, net	0	0
Deferred income taxes	(6.1)	(6.1)
Other current assets	0	0
Total current assets	(6.1)	(6.1)
Property, plant, equipment and mine development, net	0	0
Deferred income taxes	(3.1)
Investments and other assets	(9,326.9)	(8,631.1)
Total assets	(9,336.1)	(8,637.2)
Current liabilities
Current maturities of long-term debt	0	0
Payables to (receivables from) affiliates, net	0	0
Liabilities from coal trading activities, net	0	0
Deferred income taxes	(6.1)	(6.1)
Accounts payable and accrued expenses	0	0
Total current liabilities	(6.1)	(6.1)
Long-term debt, less current maturities	0	0
Deferred income taxes	(3.1)	0
Notes payable to (receivables from) affiliates, net	0	0
Other noncurrent liabilities	0	0
Total liabilities	(9.2)	(6.1)
Peabody Energy Corporation's stockholders' equity	(9,326.9)	(8,631.1)
Noncontrolling interests	0	0
Total stockholders' equity	(9,326.9)	(8,631.1)
Total liabilities and stockholders' equity	$ (9,336.1)	$ (8,637.2)