Financial Instruments and Risk Management (Concentration of Credit Risk) (Details)	12 Months Ended
	Dec. 31, 2012
Accounts receivable | Largest Oil & Gas Purchasers, One
Concentration Risk [Line Items]
Concentration of credit risk	29.00%
Accounts receivable | Largest Oil & Gas Purchasers, Two
Concentration Risk [Line Items]
Concentration of credit risk	13.00%
Accounts receivable | Largest Oil & Gas Purchasers, Three
Concentration Risk [Line Items]
Concentration of credit risk	9.00%
Total operating revenues | Largest Oil & Gas Purchasers, One
Concentration Risk [Line Items]
Concentration of credit risk	27.00%
Total operating revenues | Largest Oil & Gas Purchasers, Two
Concentration Risk [Line Items]
Concentration of credit risk	12.00%
Natural Gas Distribution
Concentration Risk [Line Items]
Number of customers	425,000