Supplemental Guarantor/Non-Guarantor Financial Information (Details 1) (USD $) In Millions, unless otherwise specified	Jun. 30, 2013	Dec. 31, 2012	Jun. 30, 2012	Dec. 31, 2011
Current assets
Cash and cash equivalents	$ 517.9	$ 558.8	$ 489.2	$ 799.1
Accounts receivable, net	732.2	737.8
Inventories	581.6	548.4
Assets from coal trading activities, net	56.6	52.4
Deferred Tax Assets, Net of Valuation Allowance, Current	39.4	56.4
Other current assets	321.5	621.7
Total current assets	2,249.2	2,575.5
Property, plant, equipment and mine development, net	11,492.0	11,801.7
Deferred Tax Assets	0
Investments and other assets	1,186.7	1,431.8
Total assets	14,927.9	15,809.0
Current liabilities
Current maturities of long-term debt	26.0	47.8
Payables to (receivables from) affiliates, net	0	0
Deferred income taxes	2.0	0
Liabilities from coal trading activities, net	17.0	19.4
Accounts payable and accrued expenses	1,625.8	1,606.9
Total current liabilities	1,670.8	1,674.1
Long-term debt, less current maturities	5,962.0	6,205.1
Deferred income taxes	152.5	577.3
Notes (receivables from) payable to affiliates, net	0	0
Other noncurrent liabilities	2,591.5	2,413.7
Total liabilities	10,376.8	10,870.2
Peabody Energy Corporation's stockholders' equity	4,520.0	4,904.9
Noncontrolling interests	31.1	33.9
Total stockholders' equity	4,551.1	4,938.8
Total liabilities and stockholders' equity	14,927.9	15,809.0
Parent Company [Member]
Current assets
Cash and cash equivalents	333.8	269.6	86.1	283.2
Accounts receivable, net	1.3	3.6
Inventories	0	0
Assets from coal trading activities, net	0	0
Deferred Tax Assets, Net of Valuation Allowance, Current	0	0
Other current assets	2.8	275.0
Total current assets	337.9	548.2
Property, plant, equipment and mine development, net	0	0
Deferred Tax Assets	184.8
Investments and other assets	11,716.1	9,524.7
Total assets	12,238.8	10,072.9
Current liabilities
Current maturities of long-term debt	0	0
Payables to (receivables from) affiliates, net	294.0	2,309.3
Deferred income taxes	3.2	3.2
Liabilities from coal trading activities, net	0	0
Accounts payable and accrued expenses	152.9	63.3
Total current liabilities	450.1	2,375.8
Long-term debt, less current maturities	5,948.7	6,114.5
Deferred income taxes	0	43.2
Notes (receivables from) payable to affiliates, net	1,032.6	(3,421.3)
Other noncurrent liabilities	287.4	55.8
Total liabilities	7,718.8	5,168.0
Peabody Energy Corporation's stockholders' equity	4,520.0	4,904.9
Noncontrolling interests	0	0
Total stockholders' equity	4,520.0	4,904.9
Total liabilities and stockholders' equity	12,238.8	10,072.9
Guarantor Subsidiaries [Member]
Current assets
Cash and cash equivalents	0.2	0.3	159.5	0.8
Accounts receivable, net	73.7	5.0
Inventories	260.1	271.4
Assets from coal trading activities, net	95.0	87.5
Deferred Tax Assets, Net of Valuation Allowance, Current	35.5	57.3
Other current assets	43.6	0
Total current assets	508.1	421.5
Property, plant, equipment and mine development, net	4,981.3	5,120.8
Deferred Tax Assets	0
Investments and other assets	7.4	0
Total assets	5,496.8	5,542.3
Current liabilities
Current maturities of long-term debt	0.1	0
Payables to (receivables from) affiliates, net	(593.9)	(2,904.4)
Deferred income taxes	0	0
Liabilities from coal trading activities, net	4.3	4.0
Accounts payable and accrued expenses	663.4	595.0
Total current liabilities	73.9	(2,305.4)
Long-term debt, less current maturities	6.5	6.6
Deferred income taxes	106.2	142.0
Notes (receivables from) payable to affiliates, net	(6,176.0)	(1,100.4)
Other noncurrent liabilities	1,887.1	1,893.9
Total liabilities	(4,102.3)	(1,363.3)
Peabody Energy Corporation's stockholders' equity	9,599.1	6,905.6
Noncontrolling interests	0	0
Total stockholders' equity	9,599.1	6,905.6
Total liabilities and stockholders' equity	5,496.8	5,542.3
Non-Guarantor Subsidiaries [Member]
Current assets
Cash and cash equivalents	183.9	288.9	243.6	515.1
Accounts receivable, net	657.2	729.2
Inventories	321.5	277.0
Assets from coal trading activities, net	0	0
Deferred Tax Assets, Net of Valuation Allowance, Current	7.1	2.3
Other current assets	275.1	354.6
Total current assets	1,444.8	1,652.0
Property, plant, equipment and mine development, net	6,510.7	6,680.9
Deferred Tax Assets	0
Investments and other assets	1,326.9	1,037.0
Total assets	9,282.4	9,369.9
Current liabilities
Current maturities of long-term debt	25.9	47.8
Payables to (receivables from) affiliates, net	299.9	595.1
Deferred income taxes	2.0	0
Liabilities from coal trading activities, net	51.1	50.5
Accounts payable and accrued expenses	809.5	956.5
Total current liabilities	1,188.4	1,649.9
Long-term debt, less current maturities	6.8	84.0
Deferred income taxes	231.1	392.1
Notes (receivables from) payable to affiliates, net	5,143.4	4,521.7
Other noncurrent liabilities	417.0	464.0
Total liabilities	6,986.7	7,111.7
Peabody Energy Corporation's stockholders' equity	2,264.6	2,224.3
Noncontrolling interests	31.1	33.9
Total stockholders' equity	2,295.7	2,258.2
Total liabilities and stockholders' equity	9,282.4	9,369.9
Reclassifications/Eliminations [Member]
Current assets
Cash and cash equivalents	0	0
Accounts receivable, net	0	0
Inventories	0	0
Assets from coal trading activities, net	(38.4)	(35.1)
Deferred Tax Assets, Net of Valuation Allowance, Current	(3.2)	(3.2)
Other current assets	0	(7.9)
Total current assets	(41.6)	(46.2)
Property, plant, equipment and mine development, net	0	0
Deferred Tax Assets	(184.8)
Investments and other assets	(11,863.7)	(9,129.9)
Total assets	(12,090.1)	(9,176.1)
Current liabilities
Current maturities of long-term debt	0	0
Payables to (receivables from) affiliates, net	0	0
Deferred income taxes	(3.2)	(3.2)
Liabilities from coal trading activities, net	(38.4)	(35.1)
Accounts payable and accrued expenses	0	(7.9)
Total current liabilities	(41.6)	(46.2)
Long-term debt, less current maturities	0	0
Deferred income taxes	(184.8)	0
Notes (receivables from) payable to affiliates, net	0	0
Other noncurrent liabilities	0	0
Total liabilities	(226.4)	(46.2)
Peabody Energy Corporation's stockholders' equity	(11,863.7)	(9,129.9)
Noncontrolling interests	0	0
Total stockholders' equity	(11,863.7)	(9,129.9)
Total liabilities and stockholders' equity	$ (12,090.1)	$ (9,176.1)