Derivatives And Hedging Activities (Outstanding Derivative Balances) (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Other Current Assets [Member]
Derivatives And Hedging Activities [Line Items]
Gross Derivative Balance	$ 30	$ 91
Cash Collateral	10	1
Total Derivative Balances	37	82
Derivative Liability Offsetting Derivative Asset	(3)	(10)
Other Noncurrent Assets [Member]
Derivatives And Hedging Activities [Line Items]
Gross Derivative Balance	103	149
Cash Collateral	0	0
Total Derivative Balances	102	140
Derivative Liability Offsetting Derivative Asset	(1)	(9)
Other Current Liabilities [Member]
Derivatives And Hedging Activities [Line Items]
Gross Derivative Balance	(47)	(48)
Cash Collateral	13	0
Total Derivative Balances	(31)	(38)
Derivative Asset Offsetting Derivative Liability	3	10
Other Noncurrent Liabilities [Member]
Derivatives And Hedging Activities [Line Items]
Gross Derivative Balance	(66)	(101)
Cash Collateral	8	3
Total Derivative Balances	(57)	(89)
Derivative Asset Offsetting Derivative Liability	1	9
Gross Derivative Balance [Member]
Derivatives And Hedging Activities [Line Items]
Total Gross Derivative Balance	20	91
Netting [Member]
Derivatives And Hedging Activities [Line Items]
Derivative Asset Offsetting Derivative Liability	0	0
Cash Collatera [lMember]
Derivatives And Hedging Activities [Line Items]
Cash Collateral	31	4
Total Derivatve Balance [Member]
Derivatives And Hedging Activities [Line Items]
Total Derivative Balances	$ 51	$ 95