Contractual Maturity of Available-for-sale Debt Securities (Detail) (USD $) In Millions, unless otherwise specified	Sep. 30, 2013
Amortized Cost
Due within one year	$ 1,989
Due after 1 year through 5 years	2,652
Due after 5 years through 10 years
Due after 10 years	7
Total	4,648
Fair Value
Due within one year	1,992
Due after 1 year through 5 years	2,654
Due after 5 years through 10 years
Due after 10 years	7
Total	$ 4,653