Fair Value Measurements (Unrealized Losses And Fair Value Of Investments With Unrealized Losses) (Details) $ in Millions	Sep. 30, 2016 USD ($) investment
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions | investment	21
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value | $	$ 13
Corporate and asset-backed debt securities
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions | investment	6
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value | $	$ 3
United States agency debt securities
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions | investment	1
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value | $	$ 1
United States treasury debt securities
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions | investment	1
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value | $	$ 2
Certificates of deposit
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions | investment	13
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value | $	$ 7