Fair Value Measurements Fair Value, Option, Quantitative Disclosures (Details) (USD $)	3 Months Ended
	Mar. 31, 2012
Fair Value, Option, Quantitative Disclosures [Line Items]
Fair Value of Derivative Assets	$ 117,000,000
Fair Value of Derivative Liabilities	178,000,000
Natural Gas | Physical Financial Fowards Futures
Fair Value, Option, Quantitative Disclosures [Line Items]
Fair Value of Derivative Assets	31,000,000	[1]
Fair Value of Derivative Liabilities	21,000,000	[1]
Natural Gas | Physical Financial Options
Fair Value, Option, Quantitative Disclosures [Line Items]
Fair Value of Derivative Assets	6,000,000
Fair Value of Derivative Liabilities	14,000,000	[1]
Electricity | Physical Financial Fowards Futures
Fair Value, Option, Quantitative Disclosures [Line Items]
Fair Value of Derivative Assets	69,000,000
Fair Value of Derivative Liabilities	17,000,000
FTRs | Physical Financial Fowards Futures
Fair Value, Option, Quantitative Disclosures [Line Items]
Fair Value of Derivative Assets	1,000,000
Fair Value of Derivative Liabilities	18,000,000
Capacity | Physical Financial Fowards Futures
Fair Value, Option, Quantitative Disclosures [Line Items]
Fair Value of Derivative Assets	9,000,000
Liquids | Physical Financial Fowards Futures
Fair Value, Option, Quantitative Disclosures [Line Items]
Fair Value of Derivative Assets	1,000,000
Fair Value of Derivative Liabilities	108,000,000
Fair Value, Option, Quantitative Disclosures, Assets | Natural Gas | Physical Financial Fowards Futures | Minimum
Fair Value, Option, Quantitative Disclosures [Line Items]
Market Price	(1)	[1],[2]
Fair Value, Option, Quantitative Disclosures, Assets | Natural Gas | Physical Financial Fowards Futures | Maximum
Fair Value, Option, Quantitative Disclosures [Line Items]
Market Price	6	[1],[2]
Fair Value, Option, Quantitative Disclosures, Assets | Natural Gas | Physical Financial Fowards Futures | Wieghted Average
Fair Value, Option, Quantitative Disclosures [Line Items]
Market Price	3	[1],[2]
Fair Value, Option, Quantitative Disclosures, Assets | Natural Gas | Physical Financial Options | Minimum
Fair Value, Option, Quantitative Disclosures [Line Items]
Market Price	2	[2]
Price Volatility	23.00%	[2],[3]
Price Correlation	100.00%	[2],[4]
Fair Value, Option, Quantitative Disclosures, Assets | Natural Gas | Physical Financial Options | Maximum
Fair Value, Option, Quantitative Disclosures [Line Items]
Market Price	5	[2]
Price Volatility	60.00%	[2],[3]
Price Correlation	100.00%	[2],[4]
Fair Value, Option, Quantitative Disclosures, Assets | Natural Gas | Physical Financial Options | Wieghted Average
Fair Value, Option, Quantitative Disclosures [Line Items]
Market Price	4	[2]
Price Volatility	30.00%	[2],[3]
Price Correlation	100.00%	[2],[4]
Fair Value, Option, Quantitative Disclosures, Assets | Electricity | Physical Financial Fowards Futures | Minimum
Fair Value, Option, Quantitative Disclosures [Line Items]
Market Price	21	[2]
Fair Value, Option, Quantitative Disclosures, Assets | Electricity | Physical Financial Fowards Futures | Maximum
Fair Value, Option, Quantitative Disclosures [Line Items]
Market Price	61	[2]
Fair Value, Option, Quantitative Disclosures, Assets | Electricity | Physical Financial Fowards Futures | Wieghted Average
Fair Value, Option, Quantitative Disclosures [Line Items]
Market Price	43	[2]
Fair Value, Option, Quantitative Disclosures, Assets | FTRs | Physical Financial Fowards Futures | Minimum
Fair Value, Option, Quantitative Disclosures [Line Items]
Market Price	(3)	[2]
Fair Value, Option, Quantitative Disclosures, Assets | FTRs | Physical Financial Fowards Futures | Maximum
Fair Value, Option, Quantitative Disclosures [Line Items]
Market Price	3	[2]
Fair Value, Option, Quantitative Disclosures, Assets | FTRs | Physical Financial Fowards Futures | Wieghted Average
Fair Value, Option, Quantitative Disclosures [Line Items]
Market Price	0	[2]
Fair Value, Option, Quantitative Disclosures, Assets | Capacity | Physical Financial Fowards Futures | Minimum
Fair Value, Option, Quantitative Disclosures [Line Items]
Market Price	95	[2]
Fair Value, Option, Quantitative Disclosures, Assets | Capacity | Physical Financial Fowards Futures | Maximum
Fair Value, Option, Quantitative Disclosures [Line Items]
Market Price	120	[2]
Fair Value, Option, Quantitative Disclosures, Assets | Capacity | Physical Financial Fowards Futures | Wieghted Average
Fair Value, Option, Quantitative Disclosures [Line Items]
Market Price	101	[2]
Fair Value, Option, Quantitative Disclosures, Assets | Liquids | Physical Financial Fowards Futures | Minimum
Fair Value, Option, Quantitative Disclosures [Line Items]
Market Price	1	[2]
Fair Value, Option, Quantitative Disclosures, Assets | Liquids | Physical Financial Fowards Futures | Maximum
Fair Value, Option, Quantitative Disclosures [Line Items]
Market Price	2	[2]
Fair Value, Option, Quantitative Disclosures, Assets | Liquids | Physical Financial Fowards Futures | Wieghted Average
Fair Value, Option, Quantitative Disclosures [Line Items]
Market Price	1	[2]
Fair Value, Option, Quantitative Disclosures, Liabilities | Natural Gas | Physical Financial Fowards Futures | Minimum
Fair Value, Option, Quantitative Disclosures [Line Items]
Market Price	(1)	[1],[2]
Fair Value, Option, Quantitative Disclosures, Liabilities | Natural Gas | Physical Financial Fowards Futures | Maximum
Fair Value, Option, Quantitative Disclosures [Line Items]
Market Price	6	[1],[2]
Fair Value, Option, Quantitative Disclosures, Liabilities | Natural Gas | Physical Financial Fowards Futures | Wieghted Average
Fair Value, Option, Quantitative Disclosures [Line Items]
Market Price	3	[1],[2]
Fair Value, Option, Quantitative Disclosures, Liabilities | Natural Gas | Physical Financial Options | Minimum
Fair Value, Option, Quantitative Disclosures [Line Items]
Market Price	(1)	[1],[2]
Price Volatility	23.00%	[2],[3]
Price Correlation	70.00%	[2],[4]
Fair Value, Option, Quantitative Disclosures, Liabilities | Natural Gas | Physical Financial Options | Maximum
Fair Value, Option, Quantitative Disclosures [Line Items]
Market Price	5	[1],[2]
Price Volatility	59.00%	[2],[3]
Price Correlation	100.00%	[2],[4]
Fair Value, Option, Quantitative Disclosures, Liabilities | Natural Gas | Physical Financial Options | Wieghted Average
Fair Value, Option, Quantitative Disclosures [Line Items]
Market Price	2	[1],[2]
Price Volatility	36.00%	[2],[3]
Price Correlation	90.00%	[2],[4]
Fair Value, Option, Quantitative Disclosures, Liabilities | Electricity | Physical Financial Fowards Futures | Minimum
Fair Value, Option, Quantitative Disclosures [Line Items]
Market Price	12	[2]
Fair Value, Option, Quantitative Disclosures, Liabilities | Electricity | Physical Financial Fowards Futures | Maximum
Fair Value, Option, Quantitative Disclosures [Line Items]
Market Price	61	[2]
Fair Value, Option, Quantitative Disclosures, Liabilities | Electricity | Physical Financial Fowards Futures | Wieghted Average
Fair Value, Option, Quantitative Disclosures [Line Items]
Market Price	41	[2]
Fair Value, Option, Quantitative Disclosures, Liabilities | FTRs | Physical Financial Fowards Futures | Minimum
Fair Value, Option, Quantitative Disclosures [Line Items]
Market Price	(6)	[2]
Fair Value, Option, Quantitative Disclosures, Liabilities | FTRs | Physical Financial Fowards Futures | Maximum
Fair Value, Option, Quantitative Disclosures [Line Items]
Market Price	5	[2]
Fair Value, Option, Quantitative Disclosures, Liabilities | FTRs | Physical Financial Fowards Futures | Wieghted Average
Fair Value, Option, Quantitative Disclosures [Line Items]
Market Price	0	[2]
Fair Value, Option, Quantitative Disclosures, Liabilities | Liquids | Physical Financial Fowards Futures | Minimum
Fair Value, Option, Quantitative Disclosures [Line Items]
Market Price	1	[2]
Fair Value, Option, Quantitative Disclosures, Liabilities | Liquids | Physical Financial Fowards Futures | Maximum
Fair Value, Option, Quantitative Disclosures [Line Items]
Market Price	3	[2]
Fair Value, Option, Quantitative Disclosures, Liabilities | Liquids | Physical Financial Fowards Futures | Wieghted Average
Fair Value, Option, Quantitative Disclosures [Line Items]
Market Price	$ 2	[2]

[1] Includes basis.

[2] Averages weighted by volume.

[3] Represents volatilities unrepresented in published markets.

[4] Represents intra-price correlations for which markets do not exist.