Business Combination (Narrative) (Details) (USD $) Share data in Millions	0 Months Ended		3 Months Ended		9 Months Ended			0 Months Ended
	Jul. 08, 2011	Jun. 08, 2011	Sep. 30, 2011	Jun. 30, 2011	Sep. 30, 2011	Sep. 30, 2010	Jun. 14, 2011	Jun. 16, 2011 Number Of Mining Complexes - Appalachia [Member]	Jun. 16, 2011 Number Of Mining Complexes - Illinois [Member]
Number of mining complexes operated								12	one
Number of mining complexes being developed								one
Purchase of common stock value							$ 3,100,000,000
Proceeds from the issuance of common stock, net		1,250,000,000			1,267,776,000
Number of shares sold	0.7	48.0
Proceeds from issuance of $2 billion in aggregate principal amount of senior notes					2,000,000,000	500,000,000
Subsequent adjustment to previously reported cost of sales				5,600,000
Revenues related to the acquired operations included in the statement of income since acquisition			295,600,000		343,600,000
Income before income taxes related to the acquired operations included in the statement of income since acquisition			34,900,000		43,600,000
Restricted cash			$ 21,400,000		$ 21,400,000