Financial and Other Derivative Instruments Financial and Other Derivative Instruments (Netting Offsets Reconciliation to Balance Sheet) (Details) - USD ($)	Sep. 30, 2015	Dec. 31, 2014
Derivative Assets
Derivative asset, gross	$ 586,000,000	$ 1,178,000,000
Collateral adjustment	(1,000,000)	0
Derivative assets, current	90,000,000	128,000,000
Derivative assets, noncurrent	48,000,000	44,000,000
Derivative Liabilities
Derivative liability, gross	(551,000,000)	(1,110,000,000)
Collateral adjustment	21,000,000	19,000,000
Derivative liabilities, current	(56,000,000)	(77,000,000)
Derivative liabilities, noncurrent	(27,000,000)	(8,000,000)
Current derivative asset
Derivative Assets
Derivative asset, gross	448,000,000	1,083,000,000
Counterparty netting	(358,000,000)	(955,000,000)
Collateral adjustment	0	0
Noncurrent derivative asset
Derivative Assets
Derivative asset, gross	138,000,000	95,000,000
Counterparty netting	(89,000,000)	(51,000,000)
Collateral adjustment	(1,000,000)	0
Current derivative liability
Derivative Liabilities
Derivative liability, gross	(419,000,000)	(1,041,000,000)
Counterparty netting	358,000,000	955,000,000
Collateral adjustment	5,000,000	9,000,000
Noncurrent derivative liability
Derivative Liabilities
Derivative liability, gross	(132,000,000)	(69,000,000)
Counterparty netting	89,000,000	51,000,000
Collateral adjustment	$ 16,000,000	$ 10,000,000