Cash, Cash Equivalents, and Marketable Securities - Summary of Contractual Maturities of Cash Equivalent and Marketable Fixed Income Securities (Detail) (USD $) In Millions, unless otherwise specified	Sep. 30, 2013
Investments Classified by Contractual Maturity Date [Line Items]
Amortized Cost	$ 5,580
Estimated Fair Value	5,584
Due within one year
Investments Classified by Contractual Maturity Date [Line Items]
Amortized Cost	2,901
Estimated Fair Value	2,902
Due after one year through five years
Investments Classified by Contractual Maturity Date [Line Items]
Amortized Cost	2,258
Estimated Fair Value	2,262
Due after five years through ten years
Investments Classified by Contractual Maturity Date [Line Items]
Amortized Cost	151
Estimated Fair Value	150
Due after ten years
Investments Classified by Contractual Maturity Date [Line Items]
Amortized Cost	270
Estimated Fair Value	$ 270