Debt Investment Maturities (Detail) (USD $) In Millions, unless otherwise specified	Sep. 30, 2013
Cost Basis
Due in one year or less	$ 25,824
Due after one year through five years	44,904
Due after five years through 10 years	4,702
Due after 10 years	1,784
Total	77,214
Estimated Fair Value
Due in one year or less	25,852
Due after one year through five years	45,042
Due after five years through 10 years	4,753
Due after 10 years	1,829
Total	$ 77,476