Financial and Other Derivative Instruments (Netting Offsets Reconciliation to Balance Sheet) (Details) - USD ($)	Dec. 31, 2018	Dec. 31, 2017
Derivative Assets
Derivative Assets	$ 663,000,000	$ 652,000,000
Collateral adjustment	(17,000,000)	(9,000,000)
Derivative asset, current	102,000,000	103,000,000
Derivative assets, noncurrent	31,000,000	51,000,000
Derivative Liabilities
Derivative Liabilities	(669,000,000)	(657,000,000)
Collateral adjustment	0	22,000,000
Derivative liabilities, current	(67,000,000)	(99,000,000)
Derivative liabilities, noncurrent	(89,000,000)	(47,000,000)
Current derivative asset
Derivative Assets
Derivative Assets	563,000,000	540,000,000
Counterparty netting	(451,000,000)	(437,000,000)
Collateral adjustment	(10,000,000)	0
Derivative asset, current	102,000,000	103,000,000
Noncurrent derivative asset
Derivative Assets
Derivative Assets	100,000,000	112,000,000
Counterparty netting	(62,000,000)	(52,000,000)
Collateral adjustment	(7,000,000)	(9,000,000)
Derivative assets, noncurrent	31,000,000	51,000,000
Current derivative liability
Derivative Liabilities
Derivative Liabilities	(518,000,000)	(558,000,000)
Counterparty netting	451,000,000	437,000,000
Collateral adjustment	0	22,000,000
Derivative liabilities, current	(67,000,000)	(99,000,000)
Noncurrent derivative liability
Derivative Liabilities
Derivative Liabilities	(151,000,000)	(99,000,000)
Counterparty netting	62,000,000	52,000,000
Collateral adjustment	0	0
Derivative liabilities, noncurrent	$ (89,000,000)	$ (47,000,000)