Derivatives and Fair Value Measurements (Details 2) (USD $) In Millions	Jun. 30, 2011	Dec. 31, 2010
Classification and amount of derivatives on a gross basis
Current Assets	$ 446.8	$ 299.3
Noncurrent Assets	429.1	393.6
Current Liabilities	5.4	12.0
Noncurrent Liabilities	2.9	0.6
Diesel fuel cash flow hedge contracts [Member] | Cash flow hedges [Member]
Classification and amount of derivatives on a gross basis
Current Assets	58.8	25.3
Noncurrent Assets	42.7	26.9
Current Liabilities	4.3	11.9
Noncurrent Liabilities	1.9	0
Cash flow hedges [Member] | Explosives cash flow hedge contracts [Member]
Classification and amount of derivatives on a gross basis
Current Assets	0.3	0.5
Noncurrent Assets	0	0.1
Current Liabilities	0.7	0.1
Noncurrent Liabilities	0.9	0.6
Cash flow hedges [Member] | Foreign currency cash flow hedge contracts [Member]
Classification and amount of derivatives on a gross basis
Current Assets	387.7	273.5
Noncurrent Assets	386.4	366.6
Current Liabilities	0.4	0
Noncurrent Liabilities	$ 0.1	$ 0