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, 2014
Investments Classified by Contractual Maturity Date [Line Items]
Amortized Cost	$ 4,250
Estimated Fair Value	4,251
Due within one year
Investments Classified by Contractual Maturity Date [Line Items]
Amortized Cost	3,101
Estimated Fair Value	3,102
Due after one year through five years
Investments Classified by Contractual Maturity Date [Line Items]
Amortized Cost	819
Estimated Fair Value	820
Due after five years through ten years
Investments Classified by Contractual Maturity Date [Line Items]
Amortized Cost	121
Estimated Fair Value	121
Due after ten years
Investments Classified by Contractual Maturity Date [Line Items]
Amortized Cost	209
Estimated Fair Value	$ 208