Business Combination (Summary Of Acquisition Related Activities) (Details) (USD $)	6 Months Ended
	Jun. 30, 2011
Consideration paid, net of cash acquired	$ 2,910,380,000
Restricted cash	15,500,000
Receivables	114,200,000
Inventories	77,500,000
Net property, plant and equipment, including mineral rights	4,516,400,000
Goodwill	425,000,000
Other assets	49,200,000
Accounts Payable	(82,400,000)
Other accrued expenses and current liabilities	(53,000,000)
Executive change in control payments	(10,000,000)
Debt	(604,800,000)
Litigation accrual	(105,300,000)
Accrued postretirement benefits	(49,400,000)
Asset retirement obligation	(80,400,000)
Deferred income taxes, net	(1,189,900,000)
Net tangible and intangible assets acquired	2,910,400,000
Other noncurrent liabilities	(34,500,000)
Coal Supply Agreement [Member]
Coal supply agreements, net	$ (77,700,000)