Debt Investment Maturities (Detail) $ in Millions	Mar. 31, 2017 USD ($)
Cost Basis
Due in one year or less	$ 16,644
Due after one year through five years	97,412
Due after five years through 10 years	6,536
Due after 10 years	1,091
Total	121,683
Estimated Fair Value
Due in one year or less	16,637
Due after one year through five years	97,250
Due after five years through 10 years	6,512
Due after 10 years	1,093
Total	$ 121,492