Valuation and Qualifying Accounts (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2011		Dec. 31, 2010		Dec. 31, 2009
Advance royalty recoupment reserve [Member]
Valuation and Qualifying Accounts
Balance at Beginning of Period	$ 19.9		$ 17.2		$ 17.2
Charged to Costs and Expenses	1.8		1.9		1.6
Deductions	(0.1)	[1]	(0.2)	[1]	(2.2)	[1]
Other	(0.3)	[2]	1.0	[2]	0.6	[2]
Balance at End of Period	21.3		19.9		17.2
Reserve for materials and supplies [Member]
Valuation and Qualifying Accounts
Balance at Beginning of Period	6.2		6.2		4.9
Charged to Costs and Expenses	3.7		0.9		3.6
Deductions	(3.4)	[1]	(0.9)	[1]	(2.3)	[1]
Other	0		0		0
Balance at End of Period	6.5		6.2		6.2
Allowance for doubtful accounts [Member]
Valuation and Qualifying Accounts
Balance at Beginning of Period	30.3		18.3		24.8
Charged to Costs and Expenses	(3.7)		26.7		7.7
Deductions	(0.4)	[1]	(6.9)	[1]	(3.6)	[1]
Other	(9.2)	[3]	(7.8)	[3]	(10.6)	[3]
Balance at End of Period	$ 17.0		$ 30.3		$ 18.3

[1] Reserves utilized, unless otherwise indicated.

[2] Balances transferred (to) from other accounts or reserves recorded as part of a property transaction or acquisition.

[3] Reflects subsequent recovery of amounts previously reserved.