Fair Value Measurements Fair Value Measurements (Details) (Fair Value, Measurements, Recurring [Member], 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]
Commodity derivatives	$ 13		$ 15
Assets, Fair Value Disclosure	119		48
Liabilities - Commodity derivatives	(120)		(156)
Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Commodity derivatives	0		0
Assets, Fair Value Disclosure	106		33
Liabilities - Commodity derivatives	0		0
Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Commodity derivatives	80		114
Assets, Fair Value Disclosure	80		114
Liabilities - Commodity derivatives	(299)		(379)
Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Commodity derivatives	2		1
Assets, Fair Value Disclosure	2		1
Liabilities - Commodity derivatives	0		0
Other [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Commodity derivatives	(69)	[1]	(100)	[1]
Assets, Fair Value Disclosure	(69)	[1]	(100)	[1]
Liabilities - Commodity derivatives	179	[1]	223	[1]
Cash Collateral, Net Receivable (Payable), Offset Against Derivative Positions	110		123
Money market mutual funds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Money market mutual funds	106	[2]	33	[2]
Money market mutual funds [Member] | Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Money market mutual funds	106	[2]	33	[2]
Money market mutual funds [Member] | Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Money market mutual funds	0	[2]	0	[2]
Money market mutual funds [Member] | Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Money market mutual funds	0	[2]	0	[2]
Money market mutual funds [Member] | Other [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Money market mutual funds	$ 0	[1],[2]	$ 0	[1],[2]

[1] Represents netting under master netting arrangements and a net cash collateral receivable of $110 million and $123 million as of June 30, 2012 and December 31, 2011, respectively.

[2] Amounts are included in cash and cash equivalents, other current assets and other assets on the Consolidated Balance Sheets. The fair value of these money market mutual funds approximates cost.