Fair Value Measurements (Assets and Liabilities Measured At Fair Value On A Recurring Basis Using Unobservable Inputs (Level 3)) (Details) - USD ($) $ in Millions	Mar. 31, 2017	Dec. 31, 2016
Fair Value Disclosures [Abstract]
Estimated fair value due in one year or less	$ 35	$ 36
Estimated fair value due after one year through three years	$ 31	$ 32