Debt Investment Maturities (Detail) (USD $) In Millions, unless otherwise specified	Mar. 31, 2012
Cost Basis
Due in one year or less	$ 22,282
Due after one year through five years	28,547
Due after five years through 10 years	3,139
Due after 10 years	2,355
Total	56,323
Estimated Fair Value
Due in one year or less	22,335
Due after one year through five years	28,661
Due after five years through 10 years	3,289
Due after 10 years	2,493
Total	$ 56,778