Fair Value Measurements (Details) (USD $)	Jun. 30, 2014	Dec. 31, 2013
Level 1
Fair Value - Other Financial Instruments
Debt estimated fair value	$ 7,200,000,000	$ 7,100,000,000
Debt carrying value	6,800,000,000	6,900,000,000
Recurring | Level 1
Assets:
Commodity derivatives	410,000,000	185,000,000
Liabilities:
Commodity derivatives	418,000,000	199,000,000
Recurring | Level 2
Assets:
Commodity derivatives	176,000,000	195,000,000
Liabilities:
Commodity derivatives	244,000,000	223,000,000
Recurring | Netting and Collateral
Assets:
Commodity derivatives	(553,000,000)	(329,000,000)
Liabilities:
Commodity derivatives	(578,000,000)	(364,000,000)
Recurring | Total Fair Value
Assets:
Commodity derivatives	33,000,000	51,000,000
Liabilities:
Commodity derivatives	$ 84,000,000	$ 58,000,000