Derivatives And Hedging Activities (Outstanding Derivative Balances) (Details) - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2015
Other Current Assets [Member]
Derivatives And Hedging Activities [Line Items]
Gross Derivative Balance	$ 91	$ 97
Cash Collateral	1	25
Total Derivative Balances	82	118
Derivative Liability Offsetting Derivative Asset	(10)	(4)
Other Noncurrent Assets [Member]
Derivatives And Hedging Activities [Line Items]
Gross Derivative Balance	149	172
Cash Collateral	0	0
Total Derivative Balances	140	170
Derivative Liability Offsetting Derivative Asset	(9)	(2)
Other Current Liabilities [Member]
Derivatives And Hedging Activities [Line Items]
Gross Derivative Balance	(48)	(102)
Cash Collateral	0	44
Total Derivative Balances	(38)	(54)
Derivative Asset Offsetting Derivative Liability	10	4
Other Noncurrent Liabilities [Member]
Derivatives And Hedging Activities [Line Items]
Gross Derivative Balance	(101)	(140)
Cash Collateral	3	21
Total Derivative Balances	(89)	(117)
Derivative Asset Offsetting Derivative Liability	9	2
Gross Derivative Balance [Member]
Derivatives And Hedging Activities [Line Items]
Total Gross Derivative Balance	91	27
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	4	90
Total Derivatve Balance [Member]
Derivatives And Hedging Activities [Line Items]
Total Derivative Balances	$ 95	$ 117