Financial Instruments and Risk Management (Concentration of Credit Risk) (Details)	Dec. 31, 2011
Accounts receivable | Largest Oil & Gas Purchasers, One
Concentration Risk [Line Items]
Concentration of credit risk	23.00%
Accounts receivable | Largest Oil & Gas Purchasers, Two
Concentration Risk [Line Items]
Concentration of credit risk	15.00%
Accounts receivable | Largest Oil & Gas Purchasers, Three
Concentration Risk [Line Items]
Concentration of credit risk	14.00%
Accounts receivable | Largest Oil & Gas Purchasers, Four
Concentration Risk [Line Items]
Concentration of credit risk	10.00%
Accounts receivable | Other Oil & Gas Purchasers
Concentration Risk [Line Items]
Concentration of credit risk	7.00%
Total operating revenues | Largest Oil & Gas Purchasers, One
Concentration Risk [Line Items]
Concentration of credit risk	15.00%
Total operating revenues | Largest Oil & Gas Purchasers, Two
Concentration Risk [Line Items]
Concentration of credit risk	14.00%
Natural Gas Distribution
Concentration Risk [Line Items]
Number of customers	428,000