Derivative Instruments Detail 4 (Details) (USD $) In Millions, unless otherwise specified	Mar. 31, 2013		Dec. 31, 2012
Derivative Instruments Subject to Master Netting Arrangement [Line Items]
Derivative, Fair Value, Gross Amount Not Offset Against Collateral, Net	$ (221)		$ (213)
Derivative, Fair Value, Amount Subject to Master Netting Arrangement, Net, Total	0		0
Derivative, Collateral, Obligation to Return Cash	(1)	[1],[2]	(11)	[1],[2]
Derivative Asset, Fair Value, Amount Offset Against Collateral	40		34
Margin/Cash (Received) Posted Subject to Master Netting Arrangement	62	[3]	39	[3]
Derivative Liability, Fair Value, Amount Offset Against Collateral	(199)		(208)
Derivative, Fair Value, Amount Offset Against Collateral, Net	(159)		(174)
Derivative Liability, Fair Value, Amount Not Offset Against Collateral	(884)		(650)
Derivative Liability, Fair Value, Amount Subject to Master Netting Arrangement	622		396
Derivative, Collateral, Right to Reclaim Cash	63	[3]	46	[3]
Derivative, Collateral, Right to Reclaim Cash	257	[1]	196	[1]
Derivative Asset, Fair Value, Amount Not Offset Against Collateral	663		437
Derivative Asset, Fair Value, Amount Subject to Master Netting Arrangement	(622)		(396)
Derivative, Collateral, Obligation to Return Cash	(1)	[3]	(7)	[3]
Commodity Futures Contracts Assets, Fair Value Disclosure	(594)		(385)
Commodity Forward Contracts Assets, Fair Value Disclosure	(64)	[4]	(48)	[4]
Interest Rate Swap Assets, Fair Value Disclosure	5		4
Assets, Fair Value Disclosure	2,044		2,135
Commodity Futures Contracts Liabilities, Fair Value Disclosure	(655)		(424)
Commodity Forward Contracts Liabilities, Fair Value Disclosure	(41)	[4]	(26)	[4]
Interest Rate Swap Liabilities, Fair Value Disclosure	188		200
Liabilities, Fair Value Disclosure	885		661
Commodity Exchange Traded Futures and Swaps Contracts [Member]
Derivative Instruments Subject to Master Netting Arrangement [Line Items]
Derivative Asset, Fair Value, Amount Offset Against Collateral	0		0
Derivative Liability, Fair Value, Amount Offset Against Collateral	0		0
Derivative Liability, Fair Value, Amount Not Offset Against Collateral	(655)		(424)
Derivative Liability, Fair Value, Amount Subject to Master Netting Arrangement	593		379
Derivative, Collateral, Right to Reclaim Cash	62	[3]	45	[3]
Derivative Asset, Fair Value, Amount Not Offset Against Collateral	594		385
Derivative Asset, Fair Value, Amount Subject to Master Netting Arrangement	(593)		(379)
Derivative, Collateral, Obligation to Return Cash	(1)	[3]	(6)	[3]
Commodity Forward Contract [Member]
Derivative Instruments Subject to Master Netting Arrangement [Line Items]
Derivative Asset, Fair Value, Amount Offset Against Collateral	35		30
Derivative Liability, Fair Value, Amount Offset Against Collateral	(11)		(8)
Derivative Liability, Fair Value, Amount Not Offset Against Collateral	(41)		(26)
Derivative Liability, Fair Value, Amount Subject to Master Netting Arrangement	29		17
Derivative, Collateral, Right to Reclaim Cash	1	[3]	1	[3]
Derivative Asset, Fair Value, Amount Not Offset Against Collateral	64		48
Derivative Asset, Fair Value, Amount Subject to Master Netting Arrangement	(29)		(17)
Derivative, Collateral, Obligation to Return Cash	0	[3]	(1)	[3]
Interest Rate Swap [Member]
Derivative Instruments Subject to Master Netting Arrangement [Line Items]
Derivative Asset, Fair Value, Amount Offset Against Collateral	5		4
Derivative Liability, Fair Value, Amount Offset Against Collateral	(188)		(200)
Derivative Liability, Fair Value, Amount Not Offset Against Collateral	(188)		(200)
Derivative Liability, Fair Value, Amount Subject to Master Netting Arrangement	0		0
Derivative, Collateral, Right to Reclaim Cash	0	[3]	0	[3]
Derivative Asset, Fair Value, Amount Not Offset Against Collateral	5		4
Derivative Asset, Fair Value, Amount Subject to Master Netting Arrangement	0		0
Derivative, Collateral, Obligation to Return Cash	0	[3]	0	[3]
Fair Value, Inputs, Level 3 [Member]
Derivative Instruments Subject to Master Netting Arrangement [Line Items]
Derivative, Collateral, Obligation to Return Cash	0		0
Derivative, Collateral, Right to Reclaim Cash	0		0
Commodity Futures Contracts Assets, Fair Value Disclosure	0		0
Commodity Forward Contracts Assets, Fair Value Disclosure	(21)	[4]	(24)	[4]
Interest Rate Swap Assets, Fair Value Disclosure	0		0
Assets, Fair Value Disclosure	21		24
Commodity Futures Contracts Liabilities, Fair Value Disclosure	0		0
Commodity Forward Contracts Liabilities, Fair Value Disclosure	(8)	[4]	(8)	[4]
Interest Rate Swap Liabilities, Fair Value Disclosure	0		0
Liabilities, Fair Value Disclosure	$ 8		$ 8

[1] 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, and we do not offset amounts recognized for the right to reclaim, or the obligation to return, cash collateral with corresponding derivative instrument fair values.

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

[3] Negative balances represent margin deposits posted with us by our counterparties related to our derivative activities that are subject to a master netting arrangement. Positive balances reflect margin deposits and natural gas and power prepayments posted by us with our counterparties related to our derivative activities that are subject to a master netting arrangement. See Note 6 for a further discussion of our collateral.

[4] Includes OTC swaps and options.