Short-term Investments (Contractual Maturities Of Investments In Debt Securities Available-For-Sale) (Details) $ in Millions	Dec. 31, 2016 USD ($)
Amortized Cost
Due within one year	$ 1,061
Due after one year up to two years	482
Due after two years up to three years	362
Due after three years	133
Asset-backed securities	232
Amortized Cost	2,270
Fair Value
Due within one year	1,061
Due after one year up to two years	480
Due after two years up to three years	360
Due after three years	132
Asset-backed securities	231
Fair Value	$ 2,264