Fair Value Measurements (Net Carrying Value And Estimated Fair Value Of Available-For-Sale Marketable Securities) (Details) (USD $) In Millions, unless otherwise specified	Mar. 31, 2014
Due in one year or less, Cost	$ 522
Due in one year or less, Estimated Fair Value	521
Due after one year through three years, Cost	1,905
Due after one year through three years, Estimated Fair Value	1,908
Due after three years, Cost	236
Due after three years, Estimated Fair Value	237
Fair value of available-for-sale marketable securities, Cost	2,663
Fair value of available-for-sale marketable securities, Estimated Fair Value	$ 2,666