Financial Instruments - Contractual Maturities (Details) $ in Millions	Dec. 31, 2020 USD ($)
Amortized Cost
Due within one year	$ 52,838
Due after one year through five years	17,222
Due after five years through ten years	857
Due after ten years	2,644
Total	73,561
Estimated Fair Value
Due within one year	52,850
Due after one year through five years	17,546
Due after five years through ten years	863
Due after ten years	2,674
Total	$ 73,933