Marketable Securities (Details) (USD $) In Millions, unless otherwise specified	Mar. 31, 2014	Dec. 31, 2013
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Gross Unrealized Gain, Accumulated in Investments	$ 0	$ 1
Available-for-sale Securities, Gross Unrealized Loss, Accumulated in Investments	(10)	(2)
Available-for-sale Securities, Amortized Cost Basis	999	942
Available-for-sale Securities	989	941
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	370	395
Available-for-sale Securities, Gross Unrealized Gain, Accumulated in Investments	0	0
Available-for-sale Securities, Gross Unrealized Loss, Accumulated in Investments	0	0
Available-for-sale Securities, Debt Securities	370	395
United States Government Obligations [Member] | Maturity 1 To 5 Years [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Debt Securities, Amortized Cost Basis	89	124
Available-for-sale Securities, Gross Unrealized Gain, Accumulated in Investments	0	0
Available-for-sale Securities, Gross Unrealized Loss, Accumulated in Investments	0	0
Available-for-sale Securities, Debt Securities	89	124
Government-Sponsored Enterprise Obligations [Member] | Maturity 1 To 5 Years [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Debt Securities, Amortized Cost Basis	15	4
Available-for-sale Securities, Gross Unrealized Gain, Accumulated in Investments	0	0
Available-for-sale Securities, Gross Unrealized Loss, Accumulated in Investments	0	0
Available-for-sale Securities, Debt Securities	15	4
Corporate Debt Securities [Member] | Maturity 1 To 5 Years [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Debt Securities, Amortized Cost Basis	66	16
Available-for-sale Securities, Gross Unrealized Gain, Accumulated in Investments	0	0
Available-for-sale Securities, Gross Unrealized Loss, Accumulated in Investments	0	0
Available-for-sale Securities, Debt Securities	66	16
Other Debt Securities [Member] | Maturity Less Than 1 Year [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Debt Securities, Amortized Cost Basis	82	38
Available-for-sale Securities, Gross Unrealized Gain, Accumulated in Investments	0	0
Available-for-sale Securities, Gross Unrealized Loss, Accumulated in Investments	0	0
Available-for-sale Securities, Debt Securities	82	38
Other Debt Securities [Member] | Maturity 1 To 5 Years [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Debt Securities, Amortized Cost Basis	3	3
Available-for-sale Securities, Gross Unrealized Gain, Accumulated in Investments	0	0
Available-for-sale Securities, Gross Unrealized Loss, Accumulated in Investments	0	0
Available-for-sale Securities, Debt Securities	3	3
Equity Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Gross Unrealized Gain, Accumulated in Investments	0	1
Available-for-sale Securities, Gross Unrealized Loss, Accumulated in Investments	(10)	(2)
Available-for-sale Equity Securities, Amortized Cost Basis	374	362
Available-for-sale Securities, Equity Securities	$ 364	$ 361