Financial and Other Derivative Instruments (Netting Offsets Reconciliation to Balance Sheet) (Details) - USD ($)	Dec. 31, 2015	Dec. 31, 2014
Derivative Assets:
Derivative Assets	$ 711,000,000	$ 1,178,000,000
Collateral adjustment	(2,000,000)	0
Derivative Asset, Current	129,000,000	128,000,000
Derivative Assets, Noncurrent	54,000,000	44,000,000
Derivative Liabilities:
Derivative Liabilities	(705,000,000)	(1,110,000,000)
Counterparty netting	36,000,000	19,000,000
Derivative Liabilities, Current	(57,000,000)	(77,000,000)
Derivative Liabilities, Noncurrent	(86,000,000)	(8,000,000)
Current Derivative Asset
Derivative Assets:
Derivative Assets	570,000,000	1,083,000,000
Counterparty netting	(441,000,000)	(955,000,000)
Collateral adjustment	0	0
Noncurrent Derivative Asset
Derivative Assets:
Derivative Assets	141,000,000	95,000,000
Counterparty netting	(85,000,000)	(51,000,000)
Collateral adjustment	(2,000,000)	0
Current Derivative Liability
Derivative Liabilities:
Derivative Liabilities	(521,000,000)	(1,041,000,000)
Collateral adjustment	441,000,000	955,000,000
Counterparty netting	23,000,000	9,000,000
Noncurrent Derivative Liability
Derivative Liabilities:
Derivative Liabilities	(184,000,000)	(69,000,000)
Collateral adjustment	85,000,000	51,000,000
Counterparty netting	$ 13,000,000	$ 10,000,000