Marketable Securities (Narrative) (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2014 security
Investments, Debt and Equity Securities [Abstract]
Available-for-sale Securities, Gross Unrealized Loss, Accumulated in Investments	$ 10
Unrealized losses that arose within the last 12 months	8
Number of available-for-sale equity securities with unrealized losses (in securities)	2
Market value of the investments that have been in an unrealized loss position for less than 12 months	359
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	$ 4