Fair Value Disclosures (Fair Value Of Financial Instruments Using Unobservable Inputs (Level 3)) (Details) (USD $)	3 Months Ended
	Mar. 31, 2012
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair Value of financial instrument	4,954,000,000
Significant Unobservable Inputs (Level 3) [Member]
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair Value of financial instrument	495,000,000
Natural Gas Options [Member] | Significant Unobservable Inputs (Level 3) [Member]
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair Value of financial instrument	12,000,000
Natural Gas Physical Basis [Member] | Significant Unobservable Inputs (Level 3) [Member]
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair Value of financial instrument	2,000,000
Minimum [Member] | Natural Gas Options [Member] | Significant Unobservable Inputs (Level 3) [Member]
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Volatility factor, range	0.60
Minimum [Member] | Natural Gas Physical Basis [Member] | Significant Unobservable Inputs (Level 3) [Member]
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Congestion adder, range	0.02
Maximum [Member] | Natural Gas Options [Member] | Significant Unobservable Inputs (Level 3) [Member]
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Volatility factor, range	2.03
Maximum [Member] | Natural Gas Physical Basis [Member] | Significant Unobservable Inputs (Level 3) [Member]
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Congestion adder, range	0.43