Business Combinations (Summary Of Purchase Price Allocation) (Details) (USD $)	0 Months Ended	12 Months Ended
	Jun. 15, 2011	Dec. 31, 2011	Dec. 31, 2009	Dec. 31, 2010
Business Acquisition [Line Items]
Acquisitions of businesses, net of cash acquired	$ 2,894,400,000	$ 2,894,339,000	$ 768,819,000
Restricted cash	15,500,000
Receivables	113,200,000
Inventories	91,000,000
Net property, plant and equipment, including mineral rights	4,582,600,000
Goodwill	480,300,000
Other assets	35,900,000
Accounts payable	(86,000,000)
Other accrued expenses and current liabilities	(59,100,000)
Debt	(604,800,000)
Litigation accrual	(108,900,000)
Accrued postretirement benefits	(47,700,000)
Asset retirement obligation	(112,700,000)
Coal Supply Agreement Obligation Net		96,998,000		26,041,000
Coal supply agreements, net				(6,036,000)
Deferred income taxes, net	(1,278,900,000)
Other	(35,000,000)
Net tangible and intangible assets acquired	2,894,400,000
ICG [Member]
Business Acquisition [Line Items]
Coal Supply Agreement Obligation Net	$ 91,000,000