Financial Instruments - Contractual Maturities (Details) $ in Millions	Jun. 30, 2019 USD ($)
Amortized Cost
Due within one year	$ 24,249
Due after one year through five years	7,428
Due after five years through ten years	296
Due after ten years	966
Cash Equivalents and Marketable Fixed Income Securities, Cost	32,939
Estimated Fair Value
Due within one year	24,255
Due after one year through five years	7,467
Due after five years through ten years	296
Due after ten years	966
Cash Equivalents and Marketable Fixed Income Securities, Fair Value	$ 32,984