Marketable Securities (Narrative) (Details) (USD $) In Millions, unless otherwise specified	9 Months Ended
	Sep. 30, 2014 security
Investments, Debt and Equity Securities [Abstract]
Available-for-sale Securities, Gross Unrealized Loss, Accumulated in Investments	$ 7
Unrealized losses that arose within the last 12 months	5
Number of available-for-sale equity securities with unrealized losses (in securities)	1
Market value of the investments that have been in an unrealized loss position for less than 12 months	6
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	$ 4
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, Greater than or Equal to One Year	1