Assets and Liabilities with Recurring Fair Value Measurements (Details) (USD $) In Millions, unless otherwise specified	Jun. 30, 2012		Dec. 31, 2011
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	$ 723	[1]	$ 1,415	[1]
Margin deposits	262	[2]	140	[2]
Commodity futures contracts	923		1,043
Commodity forward contracts	278	[3]	111	[3]
Interest rate swaps	6		10
Total assets	2,192		2,719
Margin deposits held by us posted by our counterparties	45	[2],[4]	34	[2],[4]
Commodity futures contracts	745		899
Commodity forward contracts	577	[3]	204	[3]
Interest rate swaps	197		320
Liabilities, Fair Value Disclosure	1,564		1,457
Fair Value, Inputs, Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	723	[1]	1,415	[1]
Margin deposits	262		140
Commodity futures contracts	923		1,043
Commodity forward contracts	0	[3]	0	[3]
Interest rate swaps	0		0
Total assets	1,908		2,598
Margin deposits held by us posted by our counterparties	45		34
Commodity futures contracts	745		899
Commodity forward contracts	0	[3]	0	[3]
Interest rate swaps	0		0
Liabilities, Fair Value Disclosure	790		933
Fair Value, Inputs, Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	0	[1]	0	[1]
Margin deposits	0		0
Commodity futures contracts	0		0
Commodity forward contracts	252	[3]	74	[3]
Interest rate swaps	6		10
Total assets	258		84
Margin deposits held by us posted by our counterparties	0		0
Commodity futures contracts	0		0
Commodity forward contracts	541	[3]	184	[3]
Interest rate swaps	197		320
Liabilities, Fair Value Disclosure	738		504
Fair Value, Inputs, Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	0	[1]	0	[1]
Margin deposits	0		0
Commodity futures contracts	0		0
Commodity forward contracts	26	[3]	37	[3]
Interest rate swaps	0		0
Total assets	26		37
Margin deposits held by us posted by our counterparties	0		0
Commodity futures contracts	0		0
Commodity forward contracts	36	[3]	20	[3]
Interest rate swaps	0		0
Liabilities, Fair Value Disclosure	$ 36		$ 20
Physical Power [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value Inputs Quantitative Information Power	(8,000,000.0000)
Minimum [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value Inputs Quantitative Information Power	19.3000
Maximum [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value Inputs Quantitative Information Power	160.7500

[1] As of June 30, 2012 and December 31, 2011, we had cash equivalents of $574 million and $1,249 million included in cash and cash equivalents and $149 million and $166 million included in restricted cash, respectively.

[2] Balances are subject to master netting arrangements and presented on a gross basis on our Consolidated Condensed Balance Sheets. We do not offset fair value amounts recognized for derivative instruments executed with the same counterparty under a master netting arrangement for financial statement presentation.

[3] Includes OTC swaps and options.

[4] Included in other current liabilities on our Consolidated Condensed Balance Sheets.