Business Combination (Narrative) (Details) (USD $) Share data in Millions	0 Months Ended		6 Months Ended		0 Months Ended
	Jul. 08, 2011	Jun. 08, 2011	Dec. 31, 2011	Jun. 30, 2011	Jun. 15, 2011 Number Of Mining Complexes - Appalachia [Member]	Jun. 15, 2011 Number Of Mining Complexes - Illinois [Member]
Number of mining complexes operated					12	one
Purchase of common stock value				$ 3,100,000,000
Proceeds from the issuance of common stock, net		1,250,000		1,249,407,000
Number of shares sold	0.7	48.0		48.0
Proceeds from the issuance of $2.0 billion in aggregate principal amount of senior notes				2,000,000,000
Revenues related to the acquired operations included in the statement of income since acquisition				48,000,000
Income before income taxes related to the acquired operations included in the statement of income since acquisition				11,900,000
Severance costs			3,400,000	13,498,000
Restricted cash				$ 351,000,000