Fair Value Measurements Fair Value Measurements (Details) (USD $) In Millions, unless otherwise specified	Mar. 31, 2014		Dec. 31, 2013
Fair Value, Measurements, Recurring [Member]
Fair Value, Assets (Liabilities) Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, fair value disclosure	$ 183		$ 71
Fair Value, Measurements, Recurring [Member] | Level 1 [Member]
Fair Value, Assets (Liabilities) Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, fair value disclosure	168		61
Fair Value, Measurements, Recurring [Member] | Level 2 [Member]
Fair Value, Assets (Liabilities) Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, fair value disclosure	15		12
Fair Value, Measurements, Recurring [Member] | Level 3 [Member]
Fair Value, Assets (Liabilities) Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, fair value disclosure	1		2
Fair Value, Measurements, Recurring [Member] | Other [Member]
Fair Value, Assets (Liabilities) Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, fair value disclosure	(1)	[1]	(4)	[1]
Cash collateral, net receivable, offset against derivative positions	0		12
Money market mutual funds [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Assets (Liabilities) Measured on Recurring and Nonrecurring Basis [Line Items]
Money market mutual funds	168	[2]	61	[2]
Money market mutual funds [Member] | Fair Value, Measurements, Recurring [Member] | Level 1 [Member]
Fair Value, Assets (Liabilities) Measured on Recurring and Nonrecurring Basis [Line Items]
Money market mutual funds	168	[2]	61	[2]
Money market mutual funds [Member] | Fair Value, Measurements, Recurring [Member] | Level 2 [Member]
Fair Value, Assets (Liabilities) Measured on Recurring and Nonrecurring Basis [Line Items]
Money market mutual funds	0	[2]	0	[2]
Money market mutual funds [Member] | Fair Value, Measurements, Recurring [Member] | Level 3 [Member]
Fair Value, Assets (Liabilities) Measured on Recurring and Nonrecurring Basis [Line Items]
Money market mutual funds	0	[2]	0	[2]
Money market mutual funds [Member] | Fair Value, Measurements, Recurring [Member] | Other [Member]
Fair Value, Assets (Liabilities) Measured on Recurring and Nonrecurring Basis [Line Items]
Money market mutual funds	0	[1],[2]	0	[1],[2]
Commodity Contract [Member]
Fair Value, Assets (Liabilities) Measured on Recurring and Nonrecurring Basis [Line Items]
Cash collateral, net receivable, offset against derivative positions	0		12
Commodity Contract [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Assets (Liabilities) Measured on Recurring and Nonrecurring Basis [Line Items]
Commodity derivative assets	15		10
Commodity derivative liabilities	(42)		(53)
Commodity Contract [Member] | Fair Value, Measurements, Recurring [Member] | Level 1 [Member]
Fair Value, Assets (Liabilities) Measured on Recurring and Nonrecurring Basis [Line Items]
Commodity derivative assets	0		0
Commodity derivative liabilities	0		0
Commodity Contract [Member] | Fair Value, Measurements, Recurring [Member] | Level 2 [Member]
Fair Value, Assets (Liabilities) Measured on Recurring and Nonrecurring Basis [Line Items]
Commodity derivative assets	15		12
Commodity derivative liabilities	(43)		(69)
Commodity Contract [Member] | Fair Value, Measurements, Recurring [Member] | Level 3 [Member]
Fair Value, Assets (Liabilities) Measured on Recurring and Nonrecurring Basis [Line Items]
Commodity derivative assets	1		2
Commodity derivative liabilities	0		0
Commodity Contract [Member] | Fair Value, Measurements, Recurring [Member] | Other [Member]
Fair Value, Assets (Liabilities) Measured on Recurring and Nonrecurring Basis [Line Items]
Commodity derivative assets	(1)	[1]	(4)	[1]
Commodity derivative liabilities	$ 1	[1]	$ 16	[1]

[1] Represents netting under master netting arrangements and a net cash collateral receivable of $- million and $12 million as of March 31, 2014 and December 31, 2013, 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.