Marketable Securities (Investments In Debt And Equity Securities) (Details) - USD ($) $ in Millions	Dec. 31, 2015	Dec. 31, 2014
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Amortized Cost Basis	$ 879	$ 1,011
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax	4	1
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax	6	12
Fair Value	877	1,000
United States Government Obligations [Member] | Maturity Less Than 1 Year [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Debt Securities, Amortized Cost Basis	256	385
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax	0	0
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax	0	0
Available-for-sale Securities, Debt Securities	256	385
United States Government Obligations [Member] | Maturity Period After Within One Year [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Debt Securities, Amortized Cost Basis	116	93
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax	0	0
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax	0	0
Available-for-sale Securities, Debt Securities	116	93
Corporate Debt Securities [Member] | Maturity Period After Within One Year [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Debt Securities, Amortized Cost Basis	26	72
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax	0	0
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax	0	0
Available-for-sale Securities, Debt Securities	26	72
Other Debt Instruments [Member] | Maturity Less Than 1 Year [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Debt Securities, Amortized Cost Basis	182	130
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax	0	0
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax	0	0
Available-for-sale Securities, Debt Securities	182	130
Other Debt Instruments [Member] | Maturity Period After Within One Year [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Debt Securities, Amortized Cost Basis	3	3
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax	0	0
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax	0	0
Available-for-sale Securities, Debt Securities	3	3
Equity Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Equity Securities, Amortized Cost Basis	296	328
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax	4	1
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax	6	12
Available-for-sale Securities, Equity Securities	$ 294	$ 317