Financial Instruments - Contractual Maturities (Details) $ in Millions	Sep. 30, 2021 USD ($)
Amortized Cost
Due within one year	$ 38,618
Due after one year through five years	22,603
Due after five years through ten years	1,809
Due after ten years	3,958
Amortized cost	66,988
Estimated Fair Value
Due within one year	38,628
Due after one year through five years	22,735
Due after five years through ten years	1,814
Due after ten years	3,970
Estimated fair value	$ 67,147