Financial Instruments - Contractual Maturities (Details) $ in Millions	Sep. 30, 2020 USD ($)
Amortized Cost
Due within one year	$ 38,791
Due after one year through five years	16,106
Due after five years through ten years	753
Due after ten years	2,571
Amortized cost	58,221
Estimated Fair Value
Due within one year	38,803
Due after one year through five years	16,400
Due after five years through ten years	758
Due after ten years	2,597
Estimated fair value	$ 58,558