Fair Value Measurements (Assets and Liabilities Measured At Fair Value On A Recurring Basis Using Unobservable Inputs (Level 3)) (Details) - USD ($) $ in Millions	Jun. 30, 2018	Dec. 31, 2017
Fair Value Disclosures [Abstract]
Due in one year or less	$ 123	$ 107
Due after one year through three years	$ 156	$ 144