Debt Investment Maturities (Detail) $ in Millions	Sep. 30, 2017 USD ($)
Cost Basis
Due in one year or less	$ 22,611
Due after one year through five years	101,909
Due after five years through 10 years	8,121
Due after 10 years	921
Total	133,562
Estimated Fair Value
Due in one year or less	22,558
Due after one year through five years	101,734
Due after five years through 10 years	8,145
Due after 10 years	942
Total	$ 133,379