Financial Instruments And Risk Management (Summary Of Unrealized Risk Management Position By Product) (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Derivative [Line Items]
Other Derivative Contracts, Liabilities	$ 19	$ 19
Other Derivative Contracts, Net	(19)	(19)
Foreign Currency Swaps, Assets, at Fair Value	31
Foreign Currency Swaps, Liabilities, at Fair Value	1	1
Foreign Currency Swaps, at Fair value, Net	30	(1)
Risk Management and Other Derivative Guarantee Assets, at Fair Value	451	16
Risk Management and Other Derivative Guarantee Liabilities, at Fair Value	268	308
Risk Management and Other Derivative Guarantee, at Fair Value, Net	183	(292)
Oil and NGLs [Member]
Derivative [Line Items]
Price Risk Derivative Assets, at Fair Value		2
Price Risk Derivative Liabilities, at Fair Value	244	100
Price Risk Derivatives, at Fair Value, Net	(244)	(98)
Natural Gas [Member]
Derivative [Line Items]
Price Risk Derivative Assets, at Fair Value	420	14
Price Risk Derivative Liabilities, at Fair Value	4	188
Price Risk Derivatives, at Fair Value, Net	$ 416	$ (174)