Fair Value of Financial Instruments Fair Value Options Quantitative Disclosure (Details) (USD $)	Jun. 30, 2012
Fair Value, Option, Quantitative Disclosures [Line Items]
Electricity financial swaps	$ 31,000,000
Natural gas financial swaps	58,000,000
Minimum [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Electricity financial swaps	4.71
Natural gas financial swaps	3.01
Maximum [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Electricity financial swaps	55.68
Natural gas financial swaps	4.69
Weighted Average [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Electricity financial swaps	40.80
Natural gas financial swaps	$ 3.81