Fair Value Measurements Fair Value Measurements (Details) (Fair Value, Measurements, Recurring [Member], USD $) In Millions, unless otherwise specified	Dec. 31, 2013		Dec. 31, 2012
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Commodity derivative assets	$ 10		$ 9
Assets, Fair Value Disclosure	71		82
Commodity derivative liabilities	53		75
Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Commodity derivative assets	0		0
Assets, Fair Value Disclosure	61		73
Commodity derivative liabilities	0		0
Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Commodity derivative assets	12		32
Assets, Fair Value Disclosure	12		32
Commodity derivative liabilities	69		153
Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Commodity derivative assets	2		0
Assets, Fair Value Disclosure	2		0
Commodity derivative liabilities	0		0
Other [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Commodity derivative assets	(4)	[1]	(23)	[1]
Assets, Fair Value Disclosure	(4)	[1]	(23)	[1]
Commodity derivative liabilities	(16)	[1]	(78)	[1]
Net cash collateral receivable	12		55
Money market mutual funds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Money market mutual funds	61	[2]	73	[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	61	[2]	73	[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 $12 million and $55 million as of December 31, 2013 and 2012, 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.