Debt Investment Maturities (Detail) $ in Millions	Sep. 30, 2018 USD ($)
Cost Basis
Due in one year or less	$ 36,769
Due after one year through five years	69,379
Due after five years through 10 years	26,053
Due after 10 years	904
Debt investments, Cost Basis	133,105
Estimated Fair Value
Due in one year or less	36,577
Due after one year through five years	68,747
Due after five years through 10 years	25,444
Due after 10 years	883
Total	$ 131,651